Between now and mid-June the European political elite must give its answer to an existential question. Will it honour the deal it made to rescue Greece last July; or will it push the radical left government into default – effectively creating a failed state in Europe?

That this is primarily Europe’s dilemma, not Greece’s or the IMF’s, is clear after Monday’s Eurogroup. The IMF boss, Christine Lagarde, warned the Europeans that the Washington-based fund will not participate in further bailouts without a substantial debt write-off.

In turn, the Greek prime minister, Alexis Tsipras, forced through the last of the main austerity measures demanded by creditors: reforms to the pension system that will leave worse off everyone who is receiving more than €1,000 (£800) a month, and demand much higher contributions from workers in future.

However, by delaying their approval until now, the lenders have managed, once again, to push Greece towards bankruptcy. Although growth is better than predicted, tax receipts are still dire and bailout disbursements suspended.

Worse, and more insidious, the months of callous inaction have pushed the mood in Greek society into a dangerous place. A population that, two years ago, started demanding and giving printed receipts as an act of collective moral renewal, has given up on them once again. The most popular graffiti tag has become “all this political shit”.

The only thing that can end the crisis is debt restructuring. One way or another, Europe’s creditors – the taxpayers of Germany, France, the Netherlands etc – have to lose money. It may be dressed up by extending repayment dates; or it may take the form of the “haircut”, whereby the treasuries of northern Europe – and the ECB – write down the value of the €350bn they have lent Greece. But it has to happen. And that means Germany’s politicians must change their minds.

The old problem in Europe was a transnational freemarket economy with no democratic government; a central bank obliged by treaty to impose deflation; and a Germany willing to take the upside of the project – 4% unemployment versus 25% in Greece – but never to lead it. The new problem is different: when the EU overturned the will of the Greek people last year July, it became, effectively, a political entity based on force, not law.

Those applying the force were the German elite and a collection of east European countries who have in common weak democratic traditions, mafia-infested economies and rightwing electorates still traumatised by the Soviet era. Then, in a second act of force, by overturning the Dublin Treaty and letting nearly a million refugees come to Germany, Angela Merkel destroyed the coalition that had imposed the defeat on Greece. Eastern Europe has defied Merkel’s call for refugee quotas and answered her appeal for humanitarianism by putting razor wire at every border choke-point.

So, now it’s no longer about austerity: there is a three-way battle for the soul of Europe; between a beleaguered centre that’s seeing its consent to govern drain away; a resurgent nationalist and racist right; and a modernised radical left. The Greek request for debt relief poses to the European centre the question: which side are you on?

Amid this, the resurgent radical left faces tough decisions of its own. To understand why, we have to understand the source of its recent strength. Podemos came out of the millions-strong indignados movement in 2011; Syriza expanded during the “occupation of the squares” the same year. The 188,000 people who joined the Labour party during and after Corbyn’s campaign are not just trade unionists and old lefties; at their core are student activists who learned their politics during occupation movement of 2010/11, and hordes of returning Greens. Sinn Fein’s transformation and growth in Ireland is likewise driven by a grassroots protest movement against water charges.

But in every one of these left movements there is a disconnect between the political culture of the networked youth and structures and ideologies inherited from the mid-20th-century left.

Syriza, although it governs, is substantially hollowed out as a political force. Although its leaders are still prepared to say, “We do austerity under protest,” they no longer so often complete the thought “... and it will not work.”

With a vacuum on the left, what has broken through in Greece is pessimism, cynicism and economic nationalism, pooled with large amounts of suppressed anger. “Being held incommunicado in a cell drives you mad quicker than knowing you’re going to be executed,” is how they put it in the coffee bars of Athens.

Tsipras has spent so long seeking closure with Greece’s lenders that, should he achieve a debt deal by June, it may feel like victory. But unless he finds a way to rebuild the left as a combined political and social movement, it will be hollow.

To return both Greece and Europe to the path of social justice and human rights, we need, yes, some modernised left parties prepared to fight the power of capital. But we also need grassroots action to achieve things from below.

If the worst happens, and the European project falls apart, then all the left can offer is that movement from below. From Madrid to Athens to Westminster, the new breed of radical left politicians needs to understand this and break out of the mesmeric bubble of parliamentary success. Europe’s leaders are dicing with disaster – and no longer just in Athens. Europe’s people must be mobilised to ensure that neither harsh austerity nor anti-migrant racism defines the end years of this decade.