Schloss Meseberg is a Baroque-style palace that serves as the official guest house of the German federal government. It sits in an idyllic location 70 kilometres north of the capital, and on Saturday Chancellor Angela Merkel hosted Russian President Vladimir Putin on a working visit there. It was their second get-together in three months, signalling a wish by both leaders to find solutions to international issues in the face of the uncertainty US President Donald Trump has brought to global politics.

Expectations were strong that Merkel would raise her concerns about the situation in Idlib, where thousands of internally displaced Syrians are threatened by the likely upcoming battle for the city between Russian-supported Syrian government troops and the remaining rebels in the enclave. Over three hours, they discussed that topic, plus Iran, the conflict in Ukraine, and Nord Stream 2, the controversial gas pipeline project. The leaders made short statements prior to the talks, but neither gave a press statement afterwards.

Merkel and Putin have shared the international stage for over a decade and they have regularly discussed global issues in depth. But what was initially a positive relationship has become increasingly troubled since Russia’s illegal annexation of Crimea in 2014, the conflict in Eastern Ukraine and the Kremlin’s questionable involvement in Syria. Germany played a key role in levelling sanctions against the Kremlin and supported NATO measures to deter Russian military threats along its eastern border. For example, Germany serves as the framework nation for NATO’s enhanced forward presence in Lithuania.

But even in the increasingly tense times since 2014, Germany’s chancellor has retained a better connection with Putin than any other leader in Europe, or in the White House. Over and over, Merkel has attempted to find diplomatic solutions to conflicts by involving all sides in negotiations.

Merkel said that Germany and Russia (as a permanent member of the UN Security Council) shared a responsibility to find solutions to international conflicts. She stressed that many such issues couldn’t be solved without Moscow’s involvement. Merkel underlined the need for Russia to be engaged in avoiding a humanitarian catastrophe in Idlib and in working on a post-conflict order in Syria, which must include constitutional reform and elections.

While Germany and other European nations share with Russia a determination to end the war in Syria, their views on how that should be done vary significantly.

Moscow continues to support Bashar al-Assad and wants to retain its strategic foothold in the region, but it also wants to end its involvement in the conflict to save the millions of roubles that it consumes. Europe favours lasting peace, but without Assad, and seeks a return to safety and stability to allow refugees to go back.

In his short statement, Putin touched on his expectation that European governments would step up their efforts to rebuild essential infrastructure in Syria to facilitate the return of refugees from the region. Much of that infrastructure was destroyed by the Russian air force.

Both sides can use the Syrian conflict as a pressure tool. Putin knows he can use his influence over the Assad regime, especially when it comes to Idlib, while the EU knows that the Kremlin longs for better relations with the West. Showing willingness to find a solution that meets Europe’s goals in the post-war order in Syria could bring Russia a step closer to achieving that.

However, Europe expects much more from Russia than a change of approach to the war in Syria and what should follow it. The conflict in Eastern Ukraine was also an important item on Saturday’s agenda. Merkel is said to have again raised the possibility of an international peacebuilding mission being deployed to Ukraine’s conflict region, something she discussed with Putin during their meeting in Sochi in May.

A related issue is the Nord Stream 2 pipeline project which Moscow intends to have online by the end of 2019 to carry Russian gas to Germany, and from there to other parts of Europe. That will circumvent the need to transit the gas through Ukraine, which means Kiev will lose out on about US$3 billion a year in fees. Merkel changed her approach to the pipeline project recently—acknowledging its political character but continuing to support it—while Putin again ignored Merkel’s call for Ukraine to be involved in it. The Russian leader insisted that the project was ‘only economic’.

Putin knows, however, that Nord Stream 2 will play a significant role in improving relations with the rest of Europe. And improving German–Russian relations will be key to warming up general EU–Russia relations. Both will improve only if the Russian government shows willingness to de-escalate in both Syria and Ukraine. Whether Saturday’s meeting stirred discussions on that possibility remains to be seen.

The flag of the Syrian government was raised again over central Deraa on 12 July, more than seven years after the first popular demonstrations against the Assad regime broke out in the city in March 2011. The symbolism is self-evident, but perhaps even more significant is the speedy progress Syrian forces have made in their effort to reopen the main border crossing with Jordan at Nasib. ‘Reconciliation agreements’ have marked the rapid pace of advance by Syrian forces in the area, indicating that the fight has gone out of the rebel groups that held patches of territory east and north of Deraa. Anecdotal reports signal that the rebels have been persuaded to depart partly by local residents who have been convinced for some time that the struggle is unwinnable.

Other potential flashpoints remain. West of Deraa, on the volcanic plain that stretches to the Golan escarpment, another patchwork of rebel groups includes residual elements of Islamic State hemmed in by other Islamist and militia elements. Israel is keen to see Islamist forces, particularly Hezbollah, kept away from the disengagement lines west of Quneitra. West and north of Aleppo, meanwhile, Turkish forces occupy the Afrin Valley and the hill country stretching around Aleppo from the west. To the east, the territory from Menbij to the Iraqi frontier has been taken by a joint American–Kurdish operation, its future undefined. Other areas outside the Syrian government’s direct control include much of Idlib province, the destination for fighters who refuse to accept ‘reconciliation’ deals with the government.

Significantly, all the reconciliation deals have been negotiated under Russian supervision, and Russian military police and other units have monitored the local ceasefires. Russia is also acting as intermediary between Israel and Iran to ensure that Iranian-sponsored Hezbollah units are kept well back from the line of division on the Golan. Turkey’s role in the north is less easy to define; in many ways it seems to be settling in as a long-term supervisory power.

The real tinder box at the moment covers most of Idlib province south of the road running between Aleppo and Antioch. Its population has been augmented by rebels who refused to stay in the zones selected for reconciliation deals over the past three years, and the local, largely Sunni population is consequently living in pitiful conditions. Little information emerges from what is effectively a black hole, filled with rebels armed with the light weapons they took when they were evicted and free of any stabilising outside presence. Internet postings indicate sporadic clashes between al-Qaeda units and more secular competitors as well as firefights along the southern edge of the province immediately north of Hama.

In eastern Syria, stay-behind Islamic State units survive in remote parts of the steppe on either side of the Euphrates, and there have been isolated reports of engagements with Syrian forces. And, finally, there is the curious case of the stretch of Syrian territory well to the east of the Jordanian border crossing at Nasib: except for its long common border with Jordan, and the fact that it straddles the main highway link to Baghdad, it is devoid of any sizeable population or strategic interest.

All conflicts, no matter how visceral and violent, have a natural half-life. But like the civil war in Lebanon (1975–90), they can also linger senselessly. A turning point finally came in Lebanon when the Arab League, notably Saudi Arabia, stepped in as arbiter and re-established more or less the same power-sharing formula as the National Pact of 1943. In Syria, the situation is a little clearer: there is now every sign that the regime will survive and take control of virtually all the state’s territory, assuming covenants can be reached with residual occupation forces and with Syria’s allies in the conflict.

The keys to this process are Russia, Turkey and Iran. Early in the conflict, Russia and Iran read the situation correctly and identified where their interests lay. Iran had been building relations with Syria since 1979, encouraging a greater role for Shiite Islam. The Soviet Union had been a long-term backer of Syria, though at some points during the rule of Hafez al-Assad, father of the current president, it was clearly bamboozled by the country’s complicated manoeuvring. After Hafez’s death in 2000, Russia probably found his son Bashar a little easier to read. Turkey, for its part, had been a backer of Bashar al-Assad’s mildly reformist economic agenda before 2011. It switched 180 degrees in the early stages of the conflict, allowing the rebels to use the Syrian border crossings as revolving doors—a policy it came to regret when Islamic State extended its campaign of violence into Turkey.

The missing element was the major Western powers. Most of them read the protest movements of 2011 as another phase of the Arab Spring and hoped that, given the right encouragement, a tide of popular enthusiasm would sweep Bashar al-Assad out of power. This was a fatal misreading: Syria was not Tunisia or Egypt. The call for Assad to go offered no identifiable basis for a post-Assad order, but many Syrians believed that the democracies would follow through and impose a solution.

Soon the encouragement turned more lethal, with the United States beginning to provide light weaponry. While the gesture was too ineffectual to make an impact, it deprived Western democracies of any role in calming the situation. When both Turkey and the US turned a blind eye to the role of Gulf interests intent on unseating Bashar and reversing the drift towards a Shiite identity for Syria, the conflict flared to peak intensity.

Perhaps a few lessons have been learned, but they may not be enough. The US presence in the northeast and its enigmatic foothold in the south may be a Pentagon armchair strategist’s idea of a claim to a seat at the final negotiations. But even a token presence can bring dangerous and unexpected outcomes. By inserting itself between Turkey, the Kurds, the local Arabs and the Syrian government, the US faces home-grown skills way out of its league.

In a recent paper for the Hoover Institution, the French political geographer Fabrice Balanche notes that all scenarios in the northeast of Syria suggest a no-win for the United States: ‘US troops could be pushed out of northern Syria, giving the Syrian regime and its allies free rein’, he writes. ‘Iran will then control the entire Syrian–Iraqi border and the corridor between Tehran and the Mediterranean Sea.’ The US strategy, once again oblivious to complex dynamics on the ground, is likely to hasten one of the very aims it professes to oppose.

Whatever credibility as a great power the US had before 2017 is now irrelevant if President Donald Trump continues to see the world as akin to a reality TV show. Whether we like it or not, Russia, by contrast, has played its role expertly and consistently. Before 2011, it was a guarded marginal player in the wider region; now it holds a master key to any solution. So, too, does Iran. Adopting tactics designed to exclude Russia and Iran is simply counterintuitive. In a regional order clumsily forged by the 2003 invasion of Iraq, the likely winners will continue to be those who know the environment and play the long game.

The missile strikes against Syrian military installations that the United States, the United Kingdom and France recently carried out, in response to the government’s apparent use of chemical weapons in the rebel-held town of Douma, have once again raised the question of when the use of force against a sovereign state is permissible. The contexts vary. Countries might use force to wage a defensive war, to exercise the ‘responsibility to protect’ against genocide or other crimes against humanity, or to prevent the acquisition or use of weapons of mass destruction. But the question is always the same: When is it right to fight?

There will always be interested parties or international lawyers contesting individual cases. Yet, among policymakers and those who advise them, there is more international consensus on the appropriate use of force than meets the eye. Spelling out the scope and limits of that consensus may help to clear the ground, both for the current debate about Syria and for debates about future cases.

At least since the controversy over NATO’s military intervention in Kosovo in 1999—in which the alliance bombed Belgrade, the Serbian capital, without authorisation from the United Nations Security Council—there has been widespread international agreement on three points. The first is that there is a difference between legality and legitimacy. The use of force can be legitimate without being technically legal; and it can be technically legal without being regarded by the world as legitimate.

The second point is that legality is determined by conformity with the provisions of the UN Charter—and only that. And the third point is that there are generally understood prudential criteria for legitimacy that enjoy widespread informal acceptance, even if they are not set in stone by any international treaty, UN Charter provision, or UN General Assembly or Security Council resolution.

Defining legality

As to legality, the UN Charter makes clear that the use of coercive military force in the territory of a sovereign state without its consent is permissible only under at least one of two conditions. The first is self-defence, as stated in Chapter VII, Article 51; the second is approval by the Security Council, as stated in Chapter VII and Chapter VIII (for cases involving the use of force by regional organisations).

In the case of self-defence, there is a longstanding debate over whether Article 51 allows for the use of force when an attack by another country is feared or threatened but has not yet occurred. To the extent that there is any consensus among international lawyers about ‘anticipatory self-defence’, as it is known, it is that the use of force is permissible when there is overwhelming evidence that an attack is imminent, provided that the response is proportionate. English allows for a neat distinction that is apparently unavailable in most other languages: acting preemptively is permissible, whereas acting preventively is not.

In cases where self-defence does not apply, the legality of a military intervention depends on Security Council approval, which can be vetoed by any of that body’s five permanent members: the United States, the United Kingdom, France, Russia and China. In the event, such vetoes can be, and often are, exercised for blatantly self-interested reasons, as Russia has clearly demonstrated in the case of Syria.

In the face of this frustration, there have been periodic attempts, particularly by US and UK government lawyers, to argue that there is an additional source of legal authority outside the UN Charter. According to this view, customary international law provides for military interventions launched in response to actual or threatened mass-atrocity crimes, particularly those involving nuclear, chemical or biological weapons.

But such arguments have no legs in the absence of significant international consensus. Ultimately, if you want a legal justification for military action, you must find it in the UN Charter.

Five tests of moral right

Putting aside legality, what principles determine the legitimacy of coercive military force? Though never formally endorsed by the UN or anyone else, five prudential criteria have become part of the general currency of international debate over the last two decades. Having originated in the 2001 report, The responsibility to protect, by the International Commission on Intervention and State Sovereignty, these criteria gained further traction in the report issued by the UN Secretary-General’s High-Level Panel on Threats, Challenges, and Change in the lead-up to the UN’s 60th anniversary summit in 2005. It is now very widely, if not universally, accepted that any use of military force must pass these five tests to be accepted as morally and politically legitimate.

The first hurdle is the seriousness of threat test. Is the threatened harm to state or human security of a kind, and sufficiently clear and serious, to justify prima facie the use of force?

Second, there is the proper purpose test. Is it clear that the primary purpose of the proposed military action is to halt or avert the threat in question, whatever other purposes or motives may be involved?

Third is the last resort test. Has every non-military option for meeting the threat in question been explored, with reasonable grounds for believing that lesser measures will not succeed?

This is followed by the proportional means test. Is the scale, duration, and intensity of the proposed military action the minimum necessary to meet the threat in question?

Finally, there is the balance of consequences test, which is probably the most important of all. Is there a reasonable chance of military action being successful in meeting the threat in question, with the consequences of action not likely to be worse than the consequences of inaction? In short, will a military intervention do more harm than good?

One of the main attractions of these criteria is that they are in no way culture- or religion-specific. Though they have an obvious pedigree in Christian ‘just war’ theory, which dates back to the early Middle Ages, they resonate equally, and are not at all inconsistent, with the world’s other major intellectual and religious traditions, including Islam, Judaism, Hinduism and Buddhism. Indeed, the Mahabharata, the great Hindu epic written centuries before the birth of Christ, offers one of the earliest discussions of a ‘just war’.

The hope is that, over time, these criteria will be applied ever more systematically by the UN Security Council and other policymakers making decisions about the use of force. To be sure, long before US President Donald Trump’s election, successive American administrations have been resistant to even informal restraints on their divine right to act as they please on the world stage. But if all parties to a decision to use force were to make good-faith efforts to address each prudential criterion with deeply considered, evidence-based arguments, then it would be reasonable to expect a consensus to emerge in the cases that warrant it.

From words to (in)action

The criteria for legitimacy also help us to analyse past interventions that remain contentious to this day. For example, the 2011 NATO-led intervention in Libya, in which Colonel Muammar al-Qaddafi was pursued all the way to the grave, raised serious questions about proportionality: arguably, force applied in pursuit of regime change exceeded what was necessary to meet the primary objective of protecting civilians from atrocities.

Conversely, the much-criticised decision not to intervene militarily in Darfur in 2003–2004 was amply justified by reference to the balance of consequences test. The conflict stemming from an intervention would have made it logistically impossible to maintain international humanitarian relief for more than two million displaced Darfuris; and the fragile North–South peace agreement, just barely holding together after 20 years of terrible conflict, would have become a dead letter.

The same criterion helps us appreciate why it could be right to intervene militarily in response to crimes against humanity in Sierra Leone or Côte d’Ivoire, but not in Russia or China, regardless of how badly those governments might behave in Chechnya or Tibet and Xinjiang. An intervention against a major power would mean full-scale war, with casualties and immiseration on a much greater scale than anything that could conceivably have been averted by such action.

This is not about double standards; it is about a realistic calculation of the balance of harm. During the eruption of violence in East Timor in 1999, for example, coercive military action against Indonesia would have been absolutely unthinkable. Only after the Indonesian government had agreed, under substantial international pressure, to allow for an external peacekeeping mission with a robust enforcement mandate did intervention become possible.

To take one final case, the criteria for legitimacy also help us articulate why it was right to invade Iraq in 1991, but not in 2003; and that would still be true even if the latter war had met all the criteria for legality—which, of course, it did not. In the First Gulf War, all of the stars were aligned—legally and morally—in favour of military action. On the legal front, Iraq’s invasion of Kuwait was an unequivocal breach of the UN Charter—and universally seen as such by the members of the Security Council.

As for legitimacy, the use of force that followed—though brutal, so far as it went—was clearly motivated by a proper purpose. It was driven by necessity, because diplomacy had failed to secure Iraq’s exit from Kuwait. It was proportional in its application, not least because the intervening troops stopped short of marching on to Baghdad once the rout from Kuwait was complete. And, in terms of the balance of consequences, the intervention did no more damage than it stopped.

Conflicting imperatives

Cases involving technically legal military action that is widely seen as illegitimate continue to arise, so it is worth asking what happens when legality and legitimacy come into conflict. Consider the NATO-led action in Libya in 2011. The US, UK and French intervention was initially endorsed by the Security Council. But the intervening powers lost international support as military operations wore on, because they were seen as having changed the focus of the operation from civilian protection to regime change.

Such cases do not raise difficult conceptual issues, but they can have dire political consequences. As a result of the Libya controversy, the Security Council consensus collapsed just when a similar situation was developing in Syria, where Assad’s forces were gunning down peaceful protestors in the streets.

Yet, more often than not, the conflict between legality and legitimacy runs in the other direction, such that an action widely seen as satisfying the criteria of legitimacy does not win Security Council authorisation, owing to an actual or threatened veto. Examples of this include NATO’s 1999 intervention in Kosovo and, arguably, the recent strikes against Syria. Many would say that legitimacy trumps legality in such cases. But in so doing, they pose a difficult dilemma for those of us who passionately believe in a rule-based international order.

That dilemma admits no simple solution. Still, I have found that the most persuasive and credible way of approaching the problem of morally compelling military action in the absence of formal legal authority is to think about it in terms of a ‘plea in mitigation’ in criminal court.

This is the kind of plea that a driver caught running a red light while his pregnant wife is about to have a baby in the back seat might make in court:

We acknowledge that we have breached the letter of the law, but we don’t challenge its applicability. And we won’t make a habit of it. It is just that in the very particular circumstances of this case, there was an overwhelming moral imperative to act as we did. Any censure should reflect that.

As such, he would ask that any sentence reflect those extenuating circumstances.

For this kind of argument to stand up in any particular international situation, the moral case must be very compelling indeed. In the case of the apparent chemical-weapons attack in Douma, the US, UK and French missile strikes were arguably justified by the horror of the indiscriminate methods used by Bashar al-Assad regime’s. There did not appear to be any other way of changing the regime’s behaviour, and the calibrated proportionality of the response has not triggered an even wider and uglier war, as many had feared.

Yet it would have been wiser to wait until unequivocal evidence emerged proving the Assad regime’s culpability. The Western allies’ failure to do so means that their appeal to the court of global opinion is much weaker than it otherwise might have been.

‘A perfectly executed strike…Could not have had a better result. Mission Accomplished.’ So tweeted US President Donald Trump just hours after more than a hundred American, French, and British cruise missiles hit three sites in Syria believed to be associated with chemical weapons production.

The mission that was ‘accomplished’ was to deliver the message that using chemical weapons would not be cost-free for those responsible. Ideally, punitive strikes such as these would deter Syria’s government, or any other, from ever using chemical weapons again in violation of the Chemical Weapons Convention.

But it is far from clear that Trump has achieved that deterrent effect. The somewhat smaller strike undertaken a year ago failed to change Syrian behaviour, and the latest attack is no more likely to do so. What Bashar al-Assad’s government achieved with chemical weapons—gaining control of rebel-held areas in Douma and eastern Ghouta—outweighed the price it paid. And it is a near-certainty that the Syrian government continues to possess chemical weapons, and could produce additional supplies without detection.

Military action to enforce the international norm against the use of chemical weapons is legitimate and welcome, as was the decision to coordinate the response with allies and to threaten additional strikes if chemical weapons were used again. It is important to signal that opposition to the use of any weapon of mass destruction is both deep and broad.

At the same time, the United States appears to have gone to considerable lengths to avoid engaging Russian and Iranian forces. This reduced the risk of escalation, but it also ruled out many potential targets, limiting the price paid by the Syrian government for what it had done. For this and other reasons, what the missile strikes accomplished should not be exaggerated.

The Syrian government could reasonably interpret US policy as follows: ‘We will stand by and do nothing while you terrorise or kill your own people so long as you do not use chemical weapons.’ In fact, this has been the case for the past seven years, as nearly a half-million Syrians have died and more than ten million have been forced from their homes. Trump’s foreign policy is not so much immoral as it is amoral.

It bears emphasising that the missile strikes were not designed to undermine the Assad regime’s long-term prospects. Thanks in large part to Russian and Iranian support, Assad is firmly in control and will likely remain so for the foreseeable future. This is a bitter pill for many to swallow, but it is the reality.

So where does this leave US policy and, for that matter, the policy of the French, British and anti-Assad Arab governments? Trump remains committed to ending America’s military presence (now some 2,000 troops) in Syria. He made this clear when he announced the missile strikes: ‘America does not seek an indefinite presence in Syria under no circumstances,’ he said. ‘As other nations step up their contributions, we look forward to the day when we can bring our warriors home.’

But if the goal is to avoid creating a situation in which the Islamic State (ISIS) or other terrorist groups could reconstitute themselves, that day remains far off. The US is reportedly attempting to persuade Egypt, Saudi Arabia, the United Arab Emirates and Jordan to create a Sunni force that would maintain order in areas liberated from ISIS. It is far from clear whether such a force will come into being, and even less certain that it could stand on its own, given these countries’ modest capabilities and extensive commitments. A considerable US military presence and involvement will still be required.

An ongoing US troop presence is also required to maintain coordination with Syrian Kurdish forces, who did most of the fighting against ISIS. But sustaining support for the Kurds without causing additional problems with Turkey, which has introduced forces into the area to weaken Kurdish control, may prove impossible. That fact calls for reducing US military reliance on access to Turkish bases.

Trump has said nothing about the plight of internally displaced Syrians. America, which accepted more than 10,000 Syrian refugees as recently as two years ago, has rolled up its welcome mat, accepting only a trickle last year. And the matter of who should pay, and how much, to support Syrian refugees and the neighbouring countries that have taken them in remains unresolved.

A final question involves diplomacy. There is no realistic hope of engineering a political transition in Damascus, but it may be possible to arrange local cease-fires and create areas where Syrian civilians (but not government forces) could live in safety. Such arrangements, however, would likely require Russian involvement and support to keep the Syrian and Iranian governments on board. Russia has acted irresponsibly of late, but there remains the chance it will choose to offer limited help, if only to hold down the costs of its Syria policy.

None of this adds up to a solution; Syria is likely to remain a broken country for years to come, with an illegitimate government that controls most but not all of the state’s territory. But limiting the violence and improving the lot of at least some Syrians might be possible if the US does not rush to leave, if Sunni governments contribute soldiers and money, and if Russia can be persuaded to play a somewhat more constructive role.