Will conspiracy theories dominate the European parliament elections in May? They’ve become worryingly rife, and liberal democrats are having a tough time countering them. Witness how swiftly the word spread on social media, soon amplified by far-right politicians in France, that the recent bilateral treaty signed in Aachen by Emmanuel Macron and Angela Merkel hid a sinister agenda: the selling out of Alsace-Lorraine to Germany, no less.

See also how the far right-dominated coalition in Italy claimed France had caused migration flows to Europe because it had “never stopped colonising” countries in Africa. (Another diplomatic spat ensued between Paris and Rome.) This came shortly after rightwing populist forces across Europe branded the UN migration pact a vehicle aimed at “importing” tens of millions of migrants to Europe. They’re apparently intent on making hay out of this in the European campaign.

By now we’re perhaps used to conspiracy theories – like ugly splashes thrown on to Europe’s tapestry of raucous, conflicting narratives. Hungary’s prime minister, Viktor Orbán, elevated them almost to a method of government with his campaign against the billionaire philanthropist George Soros. In Poland, the nationalist ruling Law and Justice party and its leader Jarosław Kaczyński have for years been peddling crackpot versions of the 2010 Smolensk plane crash, in which the president, his brother Lech Kaczyński, was killed – including the accusation that Donald Tusk, the European council president and a critic of Kaczyński, somehow bears responsibility for the tragedy.

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Brexit is itself partly the result of conspiratorial propaganda: the trope, now likely to intensify, that the EU is out to hobble Britain out of sheer spite. It’s hard to tell whether those who go about spinning alternative universes truly believe any of it. What’s clear is they believe they’ll capitalise. Hannah Arendt once wrote that lies and conspiracy theories pushed people to “seek refuge in cynicism”. It didn’t even matter whether people believed the theory or not: even if the lies were exposed, people would “admire the leaders for their superior tactical cleverness”, she wrote.

Nor is this, of course, a strictly European feature. Donald Trump leapt on “birtherism”. And remember the “Pizzagate” craziness over Hillary Clinton. Turkey’s president, Recep Tayyip Erdoğan, has been locking thousands of people up on the basis of a “plot” waged against him by the cleric Fethullah Gülen. And then there’s Vladimir Putin, who’s surely watched with glee how Russian propaganda stories about Ukraine being in the grip of a “fascist takeover” since 2014 were so eagerly picked up by left and right extremists.

But I’m particularly worried about Europe’s fast-growing conspiracy theories, given the result they might produce in a vote that could define much of the EU’s future. Though fake news can have different origins (such as Macedonian bloggers trying to make money from Trump-supporting propaganda), most of the conspiracy theories now swirling around Europe are deliberately manipulative, serve specific political agendas, and are calibrated to sow paranoia and hostility not just within populations but between nation states. Because of this, they’ll tear at the EU’s fabric.

I spent some of my teenage years in Alsace. I’m part of a generation that grew up benefiting from programmes launched by the Franco-German Youth Office founded by De Gaulle and Adenauer’s 1963 Élysée treaty (the pledge of friendship Macron and Merkel are now trying to renew). I discovered the Munich beer festival with a German exchange student whose family I was staying with in Augsburg. I was drawn to journalism after a German teacher made us read articles by Günter Wallraff, the undercover reporter who revealed the working conditions of Turkish migrants in Germany.

Europe is a multifaceted personal journey for many of us, but there was always something quasi-sacred about Franco-German reconciliation. I’m recalling this to try to convey what a shock it was that the “Alsace-Lorraine selloff” conspiracy theory lodged itself so successfully into so many minds. Nor was it reassuring that the French government was caught off-guard by this paranoid rumour.

To see an age-old territorial obsession we thought long buried suddenly re-emerge says something about how vulnerable some cornerstones of the EU project have become. Years ago such a thing would have been confined to narrow fringes – now it’s spewed out of social media and handily picked up by the French far-right leader Marine Le Pen and others. What next? The difficulties in overcoming the dispute between Greece and Macedonia (a candidate country for EU membership) already serve as a reminder of how conspiracy theories combined with historical hangovers can create a perfect storm.

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Europe is a patchwork of nations whose past is riddled with conflicts born of manipulation and paranoia, so we need to find better ways to neutralise the danger that conspiracy theories pose. It may not be enough to rely on fact-checking or exert pressure on the internet giants, as the Brussels institutions are (however rightly) doing.

Karl Popper, in his book The Open Society and Its Enemies, noted that conspiracy theories relied on the view that the universe was governed by design, and they rested on three principles: nothing happens by accident; nothing is as it seems; and everything is connected. Outlandish claims of secret cabals can arguably go further in Europe than in other parts of the world – because of our history. When voters across the continent cast their ballot in less than four months, will this form the backdrop? Signs are the danger is growing. We ought to think about it fast.

• Natalie Nougayrède is a Guardian columnist