The Trump administration’s assassination on Thursday of General Qassem Suleimani could turn out to be its biggest foreign policy blunder. The killing could lead to a war with Iranian proxies across the Middle East, belying Trump’s supposed desire to extricate the US from its endless conflicts. But its most likely immediate effect will be to ratchet up pressure on the Iraqi government to expel US troops from Iraq. And that would mean Iran extending its already substantial influence over Iraqi government and society.

The Trump administration was quick to portray the assassination as a pre-emptive strike, saying Suleimani had been “actively developing plans to attack American diplomats and service members in Iraq and throughout the region.” Earlier on Thursday, the US defence secretary, Mark Esper, had warned from Washington, “The game has changed”.

But Trump has consistently increased tensions and courted confrontation with Iran. Since he took office in January 2017, he has wavered on many foreign policy issues, but he has been dependable on one thing: he considers Iran the greatest threat to US interests in the Middle East, and the world’s biggest state sponsor of terrorism.

The current conflagration has its roots in a burgeoning protest movement in Iraq that has demanded that both Iran and the US stop interfering in the country’s affairs. The peaceful protests began in early October, and Iraqi officials, urged on by Suleimani, responded with a bloody crackdown that killed hundreds of protesters.

Iranian-allied militias and politicians responded to the protests in part by trying to divert attention to US influence in Iraq. On 27 December, the Iran-backed Kata’ib Hezbollah group fired rockets at a military base in Kirkuk, killing a US contractor and wounding several US and Iraqi troops.

The Pentagon responded with massive retaliation, launching airstrikes against five militia bases in Iraq and Syria. The strikes killed at least two dozen and wounded 50 fighters. Thus began the latest cycle of tit-for-tat violence – over a holiday weekend when most Americans were not paying attention to the news. Iraqis rallied in anger at the continued presence of 5,000 US troops in Iraq. Members of the Iraqi parliament began calling for the expulsion of US forces and an end to security cooperation with Washington.

On 31 December, thousands of militia members marched on the US embassy in Baghdad’s fortified Green Zone. Iraqi officials allowed the protesters to reach the embassy’s outer compound. The siege continued for a second day, until militia leaders called on their supporters to go home.

But the images of protesters besieging a US embassy in the Middle East embarrassed the Trump administration, which rushed to prove that it would not allow “another Benghazi”. The crisis appeared to have been resolved by Wednesday night, when the protesters left the Green Zone. But the administration was preparing a far more severe response, which unfolded last night.

Suleimani was no ordinary general or spymaster. He was perhaps the regime’s second most powerful man after the supreme leader, Ayatollah Ali Khamenei. Suleimani nurtured a cult of personality at home and abroad, as a heroic commander and military planner who engineered an expansion of Iranian influence across the Middle East, with Shia militias and clients stretching from Iraq and Syria to Lebanon and Yemen. Many Iranians and Iraqis credit him with a major role in defeating Isis. He also helped coordinate Iranian forces to prop up Bashar al-Assad’s brutal regime in Syria. There will be enormous pressure on Iran and its allies to retaliate for his killing. On Friday morning, Khamenei promised “severe revenge”.

When Trump took office, there was no US crisis with Iran. He created one – driven by hawkish advisers, many of whom had supported the invasion of Iraq in 2003, and his desire to undo one of Barack Obama’s major foreign policy accomplishments. In May 2018, Trump unilaterally withdrew the US from the Iran nuclear deal, and reimposed the US sanctions that have crippled the Iranian economy.

Trump constantly mentions his supposed desire to end US involvement in foreign wars – in Syria, Iraq and Afghanistan. But since May 2019 the Pentagon has deployed more than 14,000 troops to the Middle East. That’s when the latest escalation with Iran began, with several incidents in the Strait of Hormuz that culminated with Tehran shooting down a US drone that it claimed had violated its airspace.

At the time, the Trump administration inflated the threat posed by Iran to US troops and allies in the Middle East. John Bolton, who was then national security adviser, lobbied for a new confrontation with Iran. At Bolton’s request, the Pentagon updated its plans to send as many as 120,000 troops to confront Tehran.

Democrats in Congress objected to the administration’s warmongering, arguing that Congress had not authorised military action. Trump eventually forced Bolton to resign, but he continues to be influenced by his allies in Saudi Arabia and the United Arab Emirates, who hype the Iran threat. It’s notable that Trump rarely criticises his two allies for their destructive actions in the region, especially the Saudi-led war on Yemen.

But the Iranian regime has also miscalculated and overreached, trying to destabilise the region to inflict a cost on Saudi Arabia and the UAE for supporting Trump’s “maximum pressure” campaign. As Trump hesitated to take military action at several points, Iranian leaders made boastful statements about US weakness. In a speech in July 2018, Suleimani directly addressed Trump after he warned the Iranian president not to threaten the US. “It is beneath the dignity of our president to respond to you,” Suleimani said, in the kind of statement that increased his stature. “I, as a soldier, respond to you.”