The recent European summit in Versailles missed a great opportunity: to launch, in a symbolic place, a new postwar order for Europe. We are not dreamers; we know that joining the European Union is no walk in the park and thatthe same procedures apply, in principle, to Ukraine as to the candidate countries in the Balkans. But there was an opportunity to establish a political union that would bridge the gap between a looser association and full membership. Instead, European leaders proceeded as if regular peacetime EU procedures are still appropriate in the extreme case of war in Europe. The freedom and peace project gave way to the EU of bureaucrats and officials. But the EU is no longer the economic union of recent years; Vladimir Putin has unintentionally turned it back into the normative and institutional alliance of its founding years. It should become that again, since the task now is not only to protect Ukraine against Russian aggression, but also to strengthen the protection of its newer members, especially the Baltic states, and to include all those states that want to join the EU in that protection. What is needed is an “expanded Weimar Triangle” (which since 1991 has linked Germany, France and Poland). This would pay particular attention to the regional expansion of the security dimension within the EU. Germany, France, Poland and the Baltic states must enter into stronger security policy cooperation, if necessary also in the field of nuclear deterrence. The UK must move closer again to Europe’s political community, an association that was carelessly squandered by Brexit. But stronger protection against Russia also means that Putin’s Trojan horses, such as Viktor Orbán’s Hungary and Aleksandar Vučić’s Serbia, should be opposed more decisively. This raises questions above all about enforcing the fundamental legal commitments of Hungary’s EU membership and Serbia’s continued status as an EU candidate country. Bosnia-Herzegovina deserves special attention in this context. Serbian politicians in Belgrade and in Banja Luka (capital of the autonomous Bosnian Serb Republic) are fuelling divisive tendencies that, 30 years after the start of the war in Yugoslavia, are breaking up Bosnia-Herzegovina’s fragile confederation. They are even making a new war between country’s ethnic groups seem possible. Greater Serb separatists can be sure of the active support of the Putin regime. Putin has provided the blueprint for such shameful manoeuvres before all our eyes since 2008 in the case of Georgia, and since 2014 in Ukraine. The EU turned a blind eye to it, ignoring Kremlin provocations and the divisive manoeuvres of opponents of European unity, from Marine Le Pen to Orbán. As Putin meticulously prepared his attack plans, Europe’s energy dependence increased dramatically while German defence spending decreased. All of this was actively promoted, not least in Germany, by frontline political actors despite clear evidence of Russian neo-imperialism. This gives rise to a special obligation today. European citizens have now heard shots fired in anger and their governments are once again standing closer together in defence of democratic values and institutions. Together they have decided on sanctions against Russia and arms deliveries to Ukraine, but they cannot prevent the suffering of the Ukrainian civilian population. Just as sanctions and arms deliveries should have come, at the very latest, when the Russian army deployed on the borders of Ukraine in 2021, we must not wait now in the case of Bosnia-Herzegovina until it is too late there, too. We spoke out in 1992 for Europe to take decisive action for the besieged city of Sarajevo, in vain. Only a genocide then triggered a belated intervention, which was not followed by a stable order in the Balkans. Today, the EU should be more vigilant and declare its clear intention to include Bosnia-Herzegovina in a political community that includes assistance against possible provocations and aggression. It should support an alliance that warns the Serbian separatists and commits Croatia, like Slovenia, to support the Federation of Bosnia and Herzegovina and to participate in a stable postwar order throughout the Balkans. The Serbian government must realise that its option to join the EU will be forfeited if it jeopardises the precarious peace order in the Balkans and seeks to gain ground in the slipstream of the Ukraine war. Putin’s project of a “Russian world” famously had a precursor in Slobodan Milošević’s “Serbian world”, in which compatriots in Bosnia and Montenegro were to be brought home into the mother empire, just as ethnic Russians in Crimea and the Donbas region were brought “home” in 2014. Milošević’s dream famously ended at the international criminal court. The Serbs in Banja Luka and Belgrade must decide on which side they belong. Milorad Dodik, the Bosnian Serb leader, has refused sanctions against Russia, and Russian (and Chinese) interested parties are coming and going in Belgrade. A clear signal to Bosnia-Herzegovina, as well as to Nato member Montenegro, would show that these two states are counted as part of the democratic world and belong in an enlarged European community. Efforts to stop basing electoral laws and state administration on ethnic proportionality are increasingly resonating in Bosnian civil society, especially among the younger generation for whom ethnic nationalism offers no chance for peace and prosperity. In this way, Putin can end up inadvertently strengthening the European Union. Daniel Cohn-Bendit was chair of the Green Group in the European parliament; Timothy Garton Ash is professor of European studies at Oxford University; Ireneusz Pawel Karolewski is professor of political theory and democracy studies at Leipzig University; Claus Leggewie is Ludwig Börne professor at Gießen University