Any sound military and political strategist knows the maxim “Divide and Conquer”—“Divide et impera” in Latin and attributed to Julius Caesar.

U.S. policy towards the Middle East, however, has often been the reverse, with the result that groups that are otherwise enemies agree on one thing—opposing the United States.

This failure of strategic logic and indeed basic common sense was on full display during the George W. Bush administration. 

After the September 11, 2001 attacks, instead of using the opportunity to widen the circle of U.S. allies or at least non-enemies in the Middle East, the Bush administration declared war on “all terrorism of global reach,” not just on the Sunni terrorists responsible. That meant not seeking some sort of détente with Shiite Iran—despite its assistance in overturning the Taliban in Afghanistan and forming a replacement government—but putting Tehran in an “Axis of Evil” with North Korea and Saddam Hussein’s Iraq.

Some members of the Bush administration went further. John Bolton, then an undersecretary of state nominally tasked with arms control (he mostly did the reverse), said that Iran should “take a number,” implying it would be the next to experience regime change after Iraq. Neoconservatives worried about Iran and its expanding stockpile of low-enriched uranium, as well as its long opposition to Israel, said that “real men go to Tehran,” not Baghdad. 

The Bush administration also went back on a promise to trade leaders of the Mujaheddin-e Khalq—a militant Iranian group nurtured by Saddam that fought on Iraq’s side during the Iran-Iraq war—for members of al-Qaeda detained in Iran. Instead the U.S. gave the group protection and Bolton among others argued that the MEK could be deployed against Iran.

As a result, the U.S. helped turn the Quds Force—the elite overseas branch of Iran’s Revolutionary Guards—into a full-fledged enemy even as its removal of Saddam’s Baathist regime opened Iraq fully to Iran-backed militants, many of whom were trained in Iran during the Iran-Iraq war. Starting with the Badr Brigade, Iran has since helped shape other Iraqi militias, among them Kataib Hezbollah, whose targeting of Americans in Iraq touched off the latest escalatory spiral.

Of course, the Trump administration’s decision in 2018 to quit the Iran nuclear deal and a year later to impose an oil embargo on Iran has been the major cause of the mayhem in the region over the past nine months. 

Now, by assassinating Quds Force leader Qassem Soleimani, the Trump administration has likely foreclosed any possibility of U.S.-Iran diplomacy and sharply increased the likelihood of nuclear proliferation in the Middle East. Iran announced on Sunday that it would no longer observe the limits set in the 2015 Joint Comprehensive Plan of Action and would resume its nuclear program. That will incentivize Saudi Arabia to get nukes of its own.

It is said that George W. Bush, when he decided to invade Iraq, did not understand the difference between Sunnis and Shias. Donald Trump seems to dislike all Muslims, except those who buy American arms or host Trump properties.

In killing Soleimani, Trump has shown his ignorance of the power of martyrdom in Shia theology. To Iranians and many Arab Shia—including those who would like to get Iran out of their countries’ affairs—Soleimani was a bulwark against al-Qaeda and the Islamic State, defending the interests of a religious minority in the Middle East. Pictures of Soleimani being embraced by the Imam Hussein—the revered Shia figure martyred in the year 680 in Karbala, Iraq, by the forces of the Sunni tyrant Yazid—are circulating widely on social media. The U.S., by implication, has become Yazid.

Iran’s long-time Sunni rival, Saudi Arabia, along with Israel, encouraged Trump to quit the Iran nuclear deal and impose draconian sanctions on the country. The Saudis paid the price last September when they suffered a major attack on their biggest oil installation, reputedly at the hands of Iran. According to Iraqi caretaker Prime Minister Adel Abdul Mahdi, Soleimani had come to Baghdad to give Iran’s answer to a peace feeler from the Saudis. Saudi-Iran reconciliation would help restore stability to the Middle East; Soleimani’s killing will do the opposite.

Beyond now having to brace for Iranian retaliatory attacks on the 50,000-plus American servicemen and women in the Middle East, the U.S. and its allies will have to contend with a reinvigorated Islamic State and other Sunni militant groups. They may target the U.S. directly or carry out false flag operations that they will try to pin on the Iranians, hoping to provoke the Trump administration to bomb the Iranian homeland. If that happens, a full-scale war seems inevitable.

Already, the U.S. mission against ISIS has been suspended as American forces concentrate on their own protection against Iran and its proxies. If the 5,000 U.S. troops in Iraq are forced to leave, as appears likely given the Iraqi reaction to the killing of Soleimani on their soil, the 500 or so Americans in Syria will also likely have to quit the region, along with European troops engaged alongside their NATO ally. It will be far more difficult for the U.S. to contain ISIS if Western forces are pushed out of both Iraq and Syria. 

The humiliation of expulsion from Iraq—a country in which the United States has expended so much blood and treasure—will be extreme. Beyond Iran, whose influence in Iraq will only rise if America leaves, and Sunni extremists, the other beneficiaries will be Russia and China. Vladimir Putin and Xi Jinping will be seen as more honest and useful brokers than the United States, having wisely not chosen sides between the Sunnis and Shias and even more wisely not sought to antagonize both.

Barbara Slavin directs the Future of Iran Initiative at the Atlantic Council and tweets @BarbaraSlavin1. The views expressed here are her own.