Daniel Hannan is an MEP for South-East England, and a journalist, author, and broadcaster. His most recent book is What Next: How to Get the Best from Brexit.

In 2015, MI5 uncovered an Iranian-sponsored bomb factory in Hillingdon. Police found three metric tonnes of ammonium nitrate – the explosive material used in, among other terrorist abominations, the Oklahoma bombing.

The date is important. A few months earlier, Britain, as one of the permanent members of the UN Security Council, had struck a deal with Iran that was meant to provide for that country’s reintegration into the world community as a non-nuclear state. 2015 was arguably the high point of the international community’s policy of constructive engagement with the ayatollahs. The bomb-making operation, in other words, was not a response to British or American provocation. It was simply an example of Iran being Iran – the world’s pre-eminent exporter of violence.

There is a tendency in Britain to think of Iran simply as a regional nuisance – a threat, no doubt, to Israel, and to some of Britain’s Arab allies, but hardly a global menace. This is fundamentally to misunderstand the way the mullahs think.

Consider the following list of countries: Albania, Argentina, Bahrain, Denmark, France, India, Kenya, Thailand. What do they have in common? Only this: they have all been on the receiving end of Iranian-sponsored terrorism, most of it masterminded by the late and unlamented Qasem Soleimani.

A strange list, no? I mean, what possible interest could the Iranian state have in, say, Argentina? In 1994, a Jewish cultural centre in Buenos Aires was bombed, with 85 fatalities and hundreds of injuries. The trail led back to Teheran. What were the mullahs trying to achieve? Could it have been precisely Argentina’s distance from Iran that made it attractive? That Iran’s leaders wanted to show that they could strike anywhere? That state sovereignty, territorial jurisdiction and geographical remoteness meant nothing to them?

When we think of the 1979 Islamic Revolution, we tend to overemphasise the first word and underemphasise the second. Yes, Iran’s leaders are theocrats; but, far more immediately, they are revolutionaries, committed to spreading their revolt across the world.

Like the French revolutionaries after 1789, or the Russian revolutionaries after 1917, they immediately spilled out from behind their borders, sponsoring militias and terrorist cells on every continent.

In retrospect, their intentions were clear from their first act, namely the attack on the US embassy in Teheran. It is hard, forty years on, to emphasise quite how shocking it was to make hostages of diplomatic personnel. The sanctity of legation buildings is the cornerstone of the international order. When, for example, Gen Galtieri invaded the Falkland Islands, British diplomats in Buenos Aires never seriously feared for their safety. Even during the Second World War, when barbaric dictatorships fought to destroy one another, diplomatic personnel were peacefully evacuated through neutral countries.

In refusing to recognise that norm, the ayatollahs were sending out the clearest possible signal: “Your rules don’t apply to us. We don’t recognise your notions of international law”. And so they have continued for four decades.

Their apologists in the West want to make all this about us. If only we stopped meddling in the region, they argue, there would be no blowback. If only we hadn’t backed the coup against Mohammed Mossadegh in 1953, all would have been well. If we carry on intervening, we can hardly complain when we get attacked in return. This line is taken especially strenuously by Jeremy Corbyn, a former employee of an Iranian state TV station.

But it misses the nature of the regime in Teheran. Revolutionaries are precisely that – revolutionary. Their regimes depend on a degree of overseas conflict. Again like the French and Russian revolutionaries, the Iranian revolutionaries win support at home by picking fights abroad. In Leninist terms, they export their internal contradictions. Or, to borrow a metaphor from chaos theory, they drink order from their surroundings.

During the years when the West, led by the EU, sought to draw Iran back into the comity of nations, the ayatollahs continued to sponsor militias from the Balkans to the old Silk Road Khanates. They backed terrorist bombs, cyberattacks and drone shootings. The event that immediately triggered the retaliation against Soleimani was another Iranian attack on an American embassy – this time in Iraq. Those who warn us sonorously against about “the cost of escalation” should at least acknowledge the cost of non-escalation.

During the Cold War, Western leaders were careful to stress that their quarrel was with revolutionary communism, not with the peoples of Russia, East Germany or Cuba. They were clear that the problem was communism itself: that its internal logic made it expansionist and destabilising.

Precisely the same applies today. Few nations can match Persia in the depth of their civilization. But that country’s present leaders are a menace to their people, their neighbours and everyone else. They need to be confronted and defeated.