Perfidy — deceit and treachery — has always been a principal aspect of relations between nations. Since the 18th century, the United Kingdom has often been labeled “Perfidious Albion” for its diplomatic practices. The label was usually applied by France when British diplomatic perfidy briefly exceeded that of France.

President Trump’s Monday announcement that U.S. troops would be withdrawn from northern Syria to make way for Turkish troops is a perfect example. It was both perfidious and a perfectly bad policy decision.

In 2012–13, when then-President Obama was flirting with military intervention in Syria, I was opposed to it because we had no strategic interest in Syria at that time. Since then Syria has been changed. Russia and Iran have essentially carved it up to make military bases there, and Turkey — our supposed ally but in reality an enemy — has joined in a treaty with them to keep Syrian dictator Bashar al-Assad in power.

Trump’s action is a complete betrayal of our Kurdish allies, leaving them at the mercy of Turkish troops, under the direction of Turkish President Recep Erdoğan, who will set about destroying them.

To make it worse, Trump said that while he recognized the Kurds’ efforts on our side of the Syrian war, they “were paid massive amounts of money and equipment to do so.” Trump evidently regards the Kurds as a bunch of low-level employees who can be paid off and fired at any whim, not people who have sacrificed lives fighting alongside our troops and in our cause.

After the initial announcement, Trump tried (and failed) to make it sound better by threatening to destroy the Turkish economy. He tweeted, “As I have stated strongly before, and just to reiterate, if Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will totally destroy and obliterate the economy of Turkey (I’ve done before!).”

Erdoğan has turned secular Turkey — formerly a secular state and cornerstone of NATO — into an Islamic state that is our enemy. Erdoğan is not going to take Trump’s economic threat seriously because he knows it is hollow. The U.S. Air Force base at Incirlik, near Ankara, is strategically important to our presence in the Middle East. Erdogan can — and has in the past — shut down electric power flowing to the base and can prevent air operations from it. We’re not about to obliterate his economy while Incirlik effectively remains under Turkish control.

Moreover, Erdogan has Russian and Iranian allies to help keep his economy — and his regime — afloat.

Trump’s decision is not a tactical mistake; it is a strategic error of the first magnitude.

First and foremost, every current or potential U.S. ally — in the Middle East and everywhere else — will look at what we’ve done to the Kurds and wonder why they should trust America. They will reasonably conclude that they can’t.

Erdoğan’s real allies — Russia, Iran, and Syria — will benefit more than he does from our decision to cut and run. Both Russia and Iran are firmly entrenched in Syria and have been for years. Because of Trump’s action, there is no way for us to begin to obstruct Iran’s encirclement of the Middle East generally and Israel in particular.

In addition to Russia, Iran, and Turkey, the beneficiaries include ISIS and other terrorist networks, especially Hezbollah — Iran’s Lebanese proxy. Both ISIS and al-Qaida are resurgent in Syria and will grow there unobstructed.

The most immediate result will be the release of thousands of ISIS prisoners being held in northern Syria by U.S. and Kurdish forces. According to a Fox News report, they number about 10,000. Trump has demanded that the European nations take back their many citizens among the ISIS prisoners and — unsurprisingly — they have refused. That means thousands of ISIS terrorist fighters will be set free to roam the world.

The Kurds were surprised by Trump’s sudden decision and announcements. They probably shouldn’t have been. We’ve betrayed and ignored the Kurds for the last century.

As Margaret MacMillan’s masterwork, Paris 1919, recounts, in about six months President Woodrow Wilson and the other leaders of the victorious powers of World War I divided the world and made the mess of Mesopotamia that we’re dealing with today.

The Kurds’ homeland is in what is now northern Iraq, southeastern Turkey, and a bit of northern Syria. They have been there for centuries. In 1919, the Kurds sought a homeland for themselves on some or all of that territory. They, like several other oppressed minorities, were ignored while the big powers sliced up their worlds.

The result in 1919, as MacMillan wrote, was that the Kurds were left under the governments of Ataturk in Turkey, Reza Shah in Persia, and Faisal in Iraq. None were tolerant of Kurdish autonomy, nor are their modern successors.

Two days after U.S. and coalition forces booted Saddam Hussein’s Iraqi forces from Kuwait in 1991, President George H. W. Bush said, “In my own view … the Iraqi people should put Saddam aside, and that would facilitate the resolution of all these problems that exist and certainly would facilitate the acceptance of Iraq back into the family of peace-loving nations.”

Taking that as their cue, the Kurds rebelled against Saddam’s regime. Though they had initial successes in seizing a few cities, they were soon driven back, taking heavy losses. We did nothing to help them.

Having fought alongside our troops in Syria, the Kurds are owed more than the back of our hand. We could have — and should have — established a Kurdish safe zone in northern Syria and on Turkey’s southern border to be enforced by U.S. air power when our troops eventually withdrew. That would have made it clear to Erdoğan that we mean to keep our ally safe.

We should have made it clear to Erdoğan that his invasion of northern Syria and the Kurdish region in Iraq would not be permitted. But we did not. And now we’re abandoning the Kurds to a fight they cannot win.

My favorite novelist, George MacDonald Fraser, said it all when he wrote, “There’s a point, you know, where treachery is so complete and unashamed that it becomes statesmanship.” President Trump has made himself guilty of statesmanship.