Europe is in the throes of a far-right populist resurgence, threatening mainstream politics and the very idea of European integration.

Nationalism is playing a key part in elections across the continent, while Europe waits to see how far the far right has come, and how far the European Union has left to go.

"To understand Europe and where we are today in terms of European integration and some of the phenomena we're seeing in the contemporary period, we do have to go back to that Europe that no longer exists, the post-World War II Europe," says Alina Polyakova, the director of research on Europe and Eurasia at the Atlantic Council.

INTERACTIVE: The making and breaking of Europe

In 1945, at the end of World War II, the continent had been divided by nationalism and devastated by war. But it was also ready for a new beginning.

At a meeting in the Crimean resort of Yalta, US President Franklin Roosevelt, British Prime Minister Winston Churchill and Soviet Premier Joseph Stalin marked out a joint plan for a liberated Europe.

It set in place spheres of influence for Soviet and Western interests, and would lead to the creation of East and West Germany.

"Europe was left completely economically dilapidated, struggling, and at that time, you know, if we think of where is the starting point for what we now call the European Union, in many ways it was the Marshall Plan," Polyakova says.

The 1948 Marshall Plan distributed $13bn of US aid across ravaged western Europe.

Sanctioned by President Harry S. Truman and led by his secretary of state, George Marshall, the plan had at its heart the aim of a united Europe.

"They want to see a united Europe because they think that will attract some of the eastern satellite states away from the Russians. Essentially, it's about making western Europe in America's own image and selling America to the Europeans. This is cultural imperialism," explains Richard Aldrich, a professor of international security at the University of Warwick.

Ideological struggle

In May 1950, two years after the Marshall Plan had been put into effect, France's Foreign Minister Robert Schuman laid bare the vision of European unity.

"Europe will not be made all at once, or according to a single plan. It will be built through concrete achievements which first create a de facto solidarity," Schuman declared.

A federal Europe would consolidate what the North Atlantic Treaty Organisation, NATO, had been set up to do: keep Soviet power in check.

By 1955, just weeks after West Germany entered NATO, the Soviet Union formalised the Warsaw Pact - drawing in nations from central and eastern Europe in a common counter-purpose: challenging Western domination.

Europe was once more the centre of ideological struggle.

"The European continent becomes a battleground between Anglo-American influence that's trying to uphold and expand liberal democracy, versus Soviet communism, which is really tied up with anti-fascism," Matthew Goodwin, a professor at the Royal Institute of International Affairs, explains.

By the late 1950s, the division of Europe into two ideological blocs was a political, economic and cultural reality.

The Treaty of Rome transformed the six nations of the European Coal and Steel Community into the European Economic Community. And by August 1961, the "Iron Curtain" that symbolically divided Europe in two was made real with the building of the Berlin Wall.

Eastern Europe was closing itself off from the West. But at that same time, the West was opening up to the rest of the world.

A boom

Europe was experiencing an unprecedented boom, while keeping Britain out of its increasingly wealthy club.

The European Economic Community was absorbing foreign workers, initially from southern Europe, but by the late 1950s and 1960s from countries such as Turkey and Morocco, and, in the case of Britain, from the Commonwealth.

At the beginning of 1973, after nearly three decades of looking in from the outside, Britain, along with Ireland and Denmark, finally joined the European Economic Community. The EEC had grown to nine member states.

But later that same year, a hike in the price of crude oil by the multinational oil cartel OPEC sparked an economic crisis that was part of a wider downturn in European fortunes. It would leave the so-called "guest workers" with no work and no thought of going back to where they had come from.

"It was clear that the guest workers weren't going home, and it was only when they increasingly moved out of those kind of factory-owned apartments and into mostly white working-class areas, that it became an issue because only then did it become clear that they were here to stay, and they were going to be part of society," explains Cas Mudde, the author of the Ideology of the Extreme Right.

Foreign guest workers had now become visible local fixtures. In France, this shift stirred an anti-immigrant reaction and brought disparate sections of the far right under the leadership of one man, Jean-Marie Le Pen.

"I had the feeling that France was losing its territory," he told Al Jazeera in an exclusive interview. "And that as a consequence of these failures she would know other hardships .... So from that moment on I conducted a political campaign of 'resurgence', if you will."

This self-proclaimed "resurgence" of far-right sentiment wouldn't be confined to French soil. But just as the far right looked to take advantage of anti-immigrant sentiment and economic uncertainty, their ideas would achieve a victory, but leave their parties at a loss.

Populism

Far-right parties were emerging as a political reality, while the European Economic Community was enlarging to include Spain, Portugal and Greece. The 1980s drew to a close with increasing western European unity.

But the East would experience a seismic contraction.

President Mikhail Gorbachev's perestroika reforms failed to save the Soviet Union from collapse. The West had won the ideological war, and the fall of the Berlin Wall would symbolise the end of the 20th century's "grand narrative".

The end days of communism had brought uncertainty and opportunity to Europe. Still coming to terms with the war in Yugoslavia that had seen the rise of ethno-nationalism and the disintegration of the Balkan state, leaving more than two million refugees in its wake, western Europe pressed ahead with its most ambitious plan for greater integration. It would be signed into effect in 1992 in the Dutch city of Maastricht.

As well as paving the way for a common currency - the euro - the Maastricht Treaty made the 12 member states beholden to shared economic, social and security policies. The political and economic strings of Europe were being pulled from the EU headquarters in Brussels.

The gap between governance and the governed was getting ever greater. In 1999, the European common currency - the euro - was finally launched.



But not everyone was happy with this.

The True Finns in Finland, the Sweden Democrats and the Danish People's Party were all, to some degree, vehicles for anti-EU sentiment, France's Front National refocused its own nationalist manifesto against the supra-national union, while in Britain, the UK Independence Party would begin to campaign to get Britain out of Europe.

In 2008, the financial meltdown, which had begun with a credit crisis in the US, would be a catalyst for political and social unrest across Europe and would give the far right a chance to rush in where the mainstream feared to tread.

In Greece, the simmering financial crisis boiled over into street violence. The Greek Prime Minister, George Papandreou, committed to a 110bn euro, ($119bn) bailout by the troika of the European Commission, the European Central Bank and the International Monetary Fund.

In return, Greece would be required to make drastic cuts to its public spending, reduce its budget deficit and liberalise its markets.

"I had to take these very difficult measures, I knew that many of these were unjust but otherwise our country would have fallen off the brink, we would have gone bankrupt," says George Papandreou, the former Greek prime minister.

READ MORE: Far-right MP storms Athens school over refugee classes

The 2012 elections in Greece saw Golden Dawn, a violent, openly fascist party, claim 18 seats in the Greek parliament.

But it was a coalition government of traditional left and centre-right parties that held power in Athens, and it soon set to work implementing the imposed austerity.

In France, Marine Le Pen, daughter of Jean-Marie, had taken over as leader of the Front National, shifting its emphasis to a centre-ground that had already shifted to the right.

In 2016, the British people voted to leave the European Union. It was a victory in part fuelled by nationalism, with the UK Independence Party leading the charge. As Cas Mudde says: "BREXIT was the first significant victory in foreign policy for the radical right."

The project to unite Europe, which began in the wake of a devastating war, seems to be being challenged by populist stirrings in the nations it sought to bring together.