Type in “conspiracy theories” and it is amazing what magma bubbles up. There are entire websites devoted to laying out the wildest scenarios supposedly hidden behind events from the assassinations of JFK and John Lennon to the deaths of Marilyn Monroe and Princess Diana, to 9/11; even the recent Paris attacks are the subject of online ramblings. Shocks occur, and crazy theories start swirling.

Psychologists have tried to explain the phenomenon. Some things can be so painful or traumatic that factual, documented truths are discarded and minds are sucked into half-baked conspiratorial versions. This is the things-aren’t-what-they-seem school of thought. Nothing new perhaps. But what has become most striking is the degree to which conspiracy theories now abound in the political arena.

This is one of the most striking features of the rise of the new populist or insurgent parties across Europe and beyond. The role of conspiracy theories is worth dwelling on because it points to some of the difficulties of representative, liberal democracies today. It’s useful to compare the mechanisms and put them in historical context. It is no coincidence that conspiracy theories are often used by authoritarian systems to crush dissent.

It was telling that in France, Marine Le Pen decided to cry foul after her far-right Front National party failed to win executive power in a single region in elections this month. The way she saw it the elites – lumped together in a single bloc identified as “the regime” – had conspired to block her rise. According to her vision, enemies of the FN join forces in obscure ways, hindering the will of “the people”, which Le Pen’s party claims to represent single-handedly. Never mind that what actually happened was the simple exercise of French electoral law and tactical voting – Le Pen needed to frame events in terms of victimhood.

This “us versus them” talk is not confined to the French far-right. It is a thread that runs through just about all populist, demagogic movements. In Putin’s Russia, the official rhetoric centres on the notion that western powers are intent on blocking “legitimate” Russian national ambitions abroad and dismantling the very statehood of Russia by manipulating groups from within. Similar logic has come to the fore in the Venezuela of Hugo Chávez and his successor, Nicolás Maduro – regimes prone to ascribe every domestic setback to plots fostered by the US. If “Bolivarian” revolutions stumble, as recently happened in elections, this can only have outside causes, ones that are camouflaged, the results of secret plots.

Conspiracy theories were a big feature of Soviet bloc regimes, as authors like Czeslaw Milosz and Václav Havel described. But it’s also important not to overlook that they still exist to a degree in parts of Europe’s far-left.

The “anti-elite” message of the most radical elements of Podemos in Spain and of Greece’s Syriza movement may have attractive elements – understandable in the context of economic austerity, high unemployment and deep frustration among many young people. But less emphasised is the way these movements systematically cast themselves as the victims of vague and wide-ranging forces set on undermining their political prospects.

Their language is, of course, entirely different from Le Pen’s on immigration and refugees – but there’s some convergence. She speaks of “the regime” as an enemy – not unlike Podemos, which describes Spain’s 1978 constitutional system as la casta: an entity that must be overturned in its entirety because it supposedly impedes the genuine expression of the will of the people.

If Podemos and Syriza stumble, failing to meet electoral ambitions or promises, they are tempted to blame forces external to them: the European Union, globalised capitalism or obscure lobbies. What counts is that the traditional rules of the political game are questioned and the legitimacy of representative democracy is put into doubt.

Part of the appeal of conspiracy theories is their simplicity. In a complex, changing world, it is tempting to reduce multifaceted issues to the us-and-them narrative. It is a vision that meets little contradiction because reasoned facts are sidelined by emotion. It is a binary scheme, with “the people” on one side and “the system” on the other.

“The people” are assaulted by plots prepared from inside “the system”, which can be domestic (state institutions, traditional parties) or foreign (the EU, financial markets, the Bilderberg group ... the list is long). It also thrives on the notion that a charismatic leader embodies the will of “the people”, who will ideally be consulted through online votes or public gatherings. This is where the weakening of representative democracy sets in.

Le Pen’s programme – if she comes to power – will include rule by referendum. She promises the “emancipation of the people” from “the globalists”, and denounces “the occult links that tie those who deceive” the nation – a reference to MPs. Likewise, Vladimir Putin rails against a US-led “world order” intent on crushing Russia, and he has emptied the state of all checks and balances. Once the ruler is alone at the top of the power pyramid, problems can be identified as coming only from external plots – because, in this vision, the leader is “the people”.

It’s not that those who spread conspiracy theories don’t run into resistance: western countries adopted sanctions against Russia after it sent troops into Ukraine, and Le Pen certainly has foes in France – just as it is true that Syriza came up against strong and active opposition within the EU. But what makes proponents of conspiracy theories so obsessive is that they ascribe infinite power to the entities they label as enemies: anything that goes wrong is unrelated to their own misjudgments or failings. This logic basically sets the stage for the erosion of democracy. Indeed, in a political world of conspiracy theories, there is little room for the kind of lengthy, structured dialogue, deliberation and building of compromises that representative liberal democracy – at its core – is made up of.

Dissenting voices will be expelled, and “traitors” hounded out – all in the name of “the people”. The French historian François Furet has written about how the genesis of conspiracy theories in Europe was the French revolution: genuine popular aspirations against absolute monarchy veered into a phase of terror and war because some of the leaders believed they not only led but embodied “the people” – and so were entitled to physically eliminate any obstacle. This is not to say democratic revolutions are poisoned as such – nor to say today’s democracies have no failings. But it points to the dangers when protest movements come with theories of plots that need to be foiled and critics who need to be squeezed out.