If Aleppo falls, Syria’s vicious war will take a whole new turn, one with far-reaching consequences not just for the region but for Europe too. The latest government assault on the besieged northern Syrian city, which has caused tens of thousands more people to flee in recent days, is also a defining moment for relations between the west and Russia, whose airforce is playing a key role. The defeat of anti-Assad rebels who have partially controlled the city since 2012 would leave nothing on the ground in Syria but Assad’s regime and Islamic State. And all hope of a negotiated settlement involving the Syrian opposition will vanish. This has been a longstanding Russian objective – it was at the heart of Moscow’s decision to intervene militarily four months ago.

It is hardly a coincidence that the bombardment of Aleppo, a symbol of the 2011 anti-Assad revolution, started just as peace talks were being attempted in Geneva. Predictably, the talks soon faltered. Russian military escalation in support of the Syrian army was meant to sabotage any possibility that a genuine Syrian opposition might have its say on the future of the country. It was meant to thwart any plans the west and the UN had officially laid out. And it entirely contradicted Moscow’s stated commitment to a political process to end the war.

The aftershocks will be felt far and wide. If there is one thing Europeans have learned in 2015, it is that they cannot be shielded from the effects of conflict in the Middle East. And if there is one thing they learned from the Ukraine conflict in 2014, it is that Russia can hardly be considered Europe’s friend. It is a revisionist power capable of military aggression.

In fact, as the fate of Aleppo hangs in the balance, these events have – as no other perhaps since the beginning of the war – highlighted the connections between the Syrian tragedy and the strategic weakening of Europe and the west in general. This spillover effect is something Moscow has not only paid close attention to, but also in effect fuelled. The spread of instability fits perfectly with Russia’s goal of seeking dominance by exploiting the hesitations and contradictions of those it identifies as adversaries.

Aleppo will define much of what happens next. A defeat for Syrian opposition forces would further empower Isis in the myth that it is the sole defender of Sunni Muslims – as it terrorises the population under its control. There are many tragic ironies here, not least that western strategy against Isis has officially depended on building up local Syrian opposition ground forces so that they might one day push the jihadi insurgency out of its stronghold in Raqqa. If the very people that were meant to be counted on to do that job as foot soldiers now end up surrounded and crushed in Aleppo, who will the west turn to? Russia has all along claimed it was fighting Isis – but in Aleppo it is helping to destroy those Syrian groups that have in the past proved to be efficient against Isis.

January 10, 1995: a Chechen fighter taking cover from sniper fire after the presidential palace was destroyed by Russian artillery bombardments. Photograph: Michael Evstafiev/AFP/Getty

If there were ever any doubts about Russia’s objectives in Syria, events around Aleppo will surely have cleared them.

Vladimir Putin has duplicated in Syria the strategy he applied to Chechnya: full military onslaught on populated areas so rebels are destroyed or forced out. There is a long history of links – going back to the Soviet era – between the Syrian power structure and Russian intelligence. Just as Putin’s regime physically eliminated those in Chechnya who might have been interlocutors for a negotiated peace settlement, Assad has conflated all political opposition with “terrorism”. And as there was never any settlement in Chechnya (only full-on war and destruction until the Kremlin put its own Chechen leader in place), in Putin’s view there can be no settlement in Syria with the opposition.

Russia’s strategic objectives go much further, however. Putin wants to reassert Russian power in the Middle East, but it is Europe that he really has in mind. The defining moment came in 2013, when Barack Obama gave up on airstrikes against Assad’s military bases after chemical weapons were used. This encouraged Putin to test western resolve further away, on the European continent. Putin was certainly caught off guard by the Ukrainian Maidan popular uprising, but he swiftly moved to restore dominance through use of force, including the annexation of territory. He calculated – rightly – that his hybrid war in Ukraine could not be prevented by the west. Russian policies in Ukraine have as a result shaken the pillars of Europe’s post-cold-war security order – which Putin would like to see rewritten to Russia’s advantage.

Likewise, Russian military involvement in Syria has put Nato in a bind, with one of its key members right on the frontline. Turkey’s relations with Russia have been on the brink for months. Now Moscow has openly warned Turkey against sending forces into Syria to defend Aleppo. How the Turkish leader will choose to react is another western headache.

All this is happening at a time when European governments are desperate to win Ankara’s cooperation on the refugee problem. If Turkey now turns into a troublemaker for Nato on its Middle Eastern flank, that serves Russian interests. Similarly, if Europe sees a new exodus of refugees, Russia will stand to benefit.The refugee crisis has sowed deep divisions on the continent and it has helped populist rightwing parties flourish – many of which are Moscow’s political allies against the EU as a project. The refugee crisis has put key EU institutions under strain; it has heightened the danger of Brexit (which Moscow would welcome); and it has severely weakened Angela Merkel, the architect of European sanctions against Russia.

Of course, it would be an exaggeration to say that Putin had all this worked out from the start. He has been led by events as much as he has wanted to control them. Russia is not responsible for the outbreak of the civil war in Syria, nor does it have its hand in everything that happens in Ukraine. But the way Russia has cynically played its pawns should send more alarm bells ringing in the west and in the UN than is the case now.

Putin likes to cast himself as a man of order, but his policies have brought more chaos, and Europe is set to pay an increasing price. Getting the Russian regime to act otherwise will require more than wishful thinking. Aleppo is an unfolding human tragedy. But it is necessary to connect the dots between the plight of this city, Europe’s future, and how Russia hovers over both.