In defiance of international law and established rules of behavior, President Vladimir Putin’s Russia illegally annexed Crimea by force last spring and is vigorously destabilizing eastern Ukraine with a combination of military and nonmilitary means now called by specialists a “hybrid war.”

Those of us who live in the former Soviet sphere of influence expected that the Russians would come back sooner or later. Facing this, we successfully sought NATO and EU membership, just at the right time. Such membership, especially in NATO with its Article 5 promise of collective defense, may have been enough in the 1990s, but now we see that we need a supplementary “strategic reassurance” to deter an attack from Putin’s Russia or, if necessary, to defend against one.

Once Putin was convinced that Ukraine could not be kept in Russia’s sphere of influence, he decided to break it and grab the parts that the Kremlin always considered “belonged” to it. We now are witnessing Russia’s illegal annexation of Crimea and its broader drive toward creating and controlling Novorossiya (“New Russia”), a swath of former Soviet and Tsarist possessions that stretches across much of Ukraine. Putin and other Russian leaders, as well as local “commanders” of their proxy forces in southeastern Ukraine, have openly declared this ambition.

Putin’s Russia has been modifying borders by sheer military force, setting a very negative pattern that could be supported by other states with territorial claims and grievances.

The fundamentals of Europe’s territorial status quo—including the Helsinki Accords of 1975, the 1990 Treaty on Conventional Armed Forces in Europe, and the Paris Charter of 1990—have been cynically thrown overboard. We see a forceful re-accreditation of the essential dictum of power politics: “might makes right.”

Putin is limiting the West’s, particularly NATO’s, response to his attacks in an ingenious way. He is pursuing his strategic objective, recreating Russia’s former empire through a series of tactical moves, each limited enough to avoid triggering the full response of the Alliance. NATO mobilized itself, notably in this month’s summit conference in Wales, to reassure its eastern member states, and its governments have communicated to Russia that it has to stop and ultimately reverse its seizure of Ukrainian territory.

Although this response was logical and necessary, it seems to have two flaws. First, Russia does not seem deterred, continuing its subversion and aggression; and second, it is rather illusory to wait for such a behavior, once Russia seems to have crossed the point of no return. This is illustrated by the Russian-Ukrainian cease-fire, which Putin timed for early September in an effort to water down two Western responses to his aggression that were being forged at that time. The NATO Summit was deciding its military response, and European Union leaders were discussing new sanctions against Russia. The truce reflects no intention by Russia to halt the drive toward recreating its empire.

Meanwhile, at the other end of Europe, Scotland tomorrow will vote on whether to stay in the UK or declare its independence. Whether or not the Scots choose the independent road, they could advance a process of peaceful border changing, a sharp contrast to the violent process initiated by Putin’s Russia in the east. Other regions with separatist tendencies — Catalonia, the Basque Country, and even Belgium — might be encouraged to pursue a peaceful course, as taken by Scotland.

At such a point, the EU and primarily NATO will be faced with a double challenge: how to confront the violent border changing process in Europe’s east, while trying to manage the peaceful one initiated in the west. In facing such a challenge, the US and Europe also must honestly consider how much the two processes reinforce each other, particularly the extent to which Putin’s Russia stands to gain from the fragmentation of European unity.

Unfortunately, such a mission proves tricky, as Russia is acting below the threshold imposed by Article 5, which only covers aggression — not the subversion well underway. That is why it is crucial that we try to do everything possible to avoid such a scenario.

Ioan Mircea Pascu is a member of the European Parliament and former defense minister of Romania. He serves on the Atlantic Council Strategic Advisors Group.