Tony Blair was the prime minister of Britain from 1997 to 2007.

This piece has been updated.

We view Iran as a state with an ideology; but it is more accurately seen as an ideology with a state.

The 1979 Islamic revolution in Iran was of vast consequence not only to Iran and its people, but also to the broader Middle East, to Sunni Islam as well as Shia, and to the development of extremism around the world. It continues to exert an often misunderstood and underestimated influence today.

Though brought to power with the help of liberal and leftist elements, the clerics quickly transformed the new state into a theocracy in which dissent was crushed and exported a Shia version of Islamism to wherever it could put down roots.

When radical Sunni extremists stormed Mecca later in 1979, inspired to create a Sunni version of the revolution, the rulers of Saudi Arabia put down the revolt but then reacted by adopting a much more conservative form of religious observance inside the kingdom. Externally, with the benefit of a high oil price, they expanded this conservative religious footprint around the world, including in Africa and the Far East.

Errors abounded. In 1979, the Soviet Union invaded Afghanistan, partly to thwart any Iranian advance. Iraq’s Saddam Hussein received Western support in his war against Iran, which produced more than a million casualties and stoked Tehran’s nuclear weapons ambitions.

Hussein’s removal in 2003 should have presented an opportunity for rapprochement. I remember conversations with then-President Mohammad Khatami that held out real hope. But he was sidelined, and instead Iran set about fomenting strife in Iraq and using the demise of Hussein to establish a network of influence in Iraq and expand regional hegemony.

As the possibility of a nuclear-armed Iran became real, the Obama administration tried to constrain it with the 2015 nuclear deal. Hopes that this would lead the Tehran regime to moderate its behavior have proved misplaced. The ayatollahs may have kept to the letter of the deal, but they have intensified their malign policies around the region.

In Syria they have helped save the Assad regime despite its savagery, in Lebanon they exercise power through Hezbollah, and in Iraq they seek to undermine the country’s independence. In Yemen they support the Houthi assault on the legitimate government, in the Gulf they do all they can to destabilize governments (especially Bahrain), and in the Palestinian territories they support the most intransigent and violent groups. And where Israel is concerned, they implacably oppose not only government policy but also the country’s very existence.

This hatred of Israel is not confined to the clerics. It is also the declared position of figures that the West has misidentified as “moderate.” Such views are inherent to the belief system underlying the Islamic republic.

For all these reasons it is misguided to see Iran as following the principles of realpolitik. It is ultimately defending and where possible extending ideological interests. The ideology, like its Sunni Islamist counterpart, is driven by a belief that religion — and one view of one religion — should be converted into a political system of government. Such a worldview necessarily becomes totalitarian.

This politicization of religion is the bane of the Middle East. In a world where economies succeed by being open, where migration means people mix across the boundaries of faith, and where countries and their people prosper by being open-minded, such a view of religion divides people, misdirects political energy and causes extremism.

It is also wrong to see the Middle East and its wider region through the filter of conflict between Sunni vs. Shia. The real struggle is between those who see coexistence — whether within Islam or between Islam and other faiths — as the future, and those who don’t.

The West has oscillated between containment and confrontation. But it has done both inconsistently.

What we should do instead is to combine the two. Where Iran is exercising military interference, it should be strongly pushed back. Where it is seeking influence, it should be countered. Where its proxies operate, it should be held responsible. Where its networks exist, they should be disrupted. Where its leaders are saying what is unacceptable, they should be exposed. Where the Iranian people — highly educated and connected, despite their government — are protesting for freedom, they should be supported.

Threats we do not mean should not be made. But every option should remain on the table.

Our allies in the region should know we are with them and can be depended upon. We should always hold out the hope that if the Iranian regime changes its actions, we can change. The door is never closed.

But 40 years of disappointment should make us clear-eyed. The revolution has made Iran the single biggest destabilizing force in the Middle East.

It is. of course. the Iranian people who feel this impact the most. Iran has a history with an extraordinary, rich and diverse civilization. Ultimately the people will find a way to the future without this outdated theocracy. When they do, they should know we will be with them; and we will be astonished at how the challenge of extremism in the Middle East and beyond abates.

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