In his long military career, Qassem Suleimani left the Middle East littered with corpses. Now he has finally joined them. His death has closed one gruesome chapter in the region’s endless conflicts, only to open another, which could well prove even worse.

No one can predict how this will turn out, perhaps least of all the two leading protagonists. Nothing about Donald Trump’s actions in the Middle East until now suggests that Suleimani’s assassination by drone outside Baghdad airport was part of a considered plan.

For its part, the leadership in Tehran has clearly been shocked by Trump’s dramatic leap up the escalation ladder.

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In the latest tit-for-tat round of the proxy war in Iraq, an American contractor had been killed in a rocket attack on Friday, triggering retaliatory airstrikes against Iranian-supported militia camps. This in turn led to the storming of the US embassy compound by pro-Iran militiamen, in which no one appears to have been hurt.

The Suleimani killing dispensed with proxies altogether and aimed a direct dagger thrust into the heart of Iranian power.

Trump may have thought that ordering this hit would bring the same plaudits with as little blowback as hunting down Abu Bakr al-Baghdadi, the leader of Isis. He would be wrong. The Isis caliphate had collapsed and its fighters had scattered.

The leader of the Revolutionary Guards’ Quds force, on the other hand, was a bearded icon of the Islamic Republic, arguably its second most powerful figure after the supreme leader, Ayatollah Ali Khamenei. Killing him was a blunt act of war against a substantial regional power. Its half-million-strong armed services are the most potent military force the US has faced since confronting the Chinese People’s Volunteer Army more than 60 years ago in Korea.

There was nothing inevitable about this conflict. Six years ago the legacy of loathing left by the Islamic Revolution began to fade. There was a multilateral agreement to curb Iran’s nuclear programme in 2015, and an unspoken mutual non-aggression pact with Suleimani during the shared campaign against Islamic State in Syria and Iraq.

“For a while when we were doing counter-Isis operations, we essentially had a gentleman’s agreement with him, that his forces wouldn’t target us and we wouldn’t target him,” said Kirsten Fontenrose, the former senior director for the Gulf in Trump’s national security council.

But with Trump’s abrogation of the 2015 nuclear deal and the collapse of the Isis caliphate, which largely removed a common foe, it was Suleimani who emerged as the US’s arch-enemy.

“He was a target of opportunity,” Fontenrose said. “When you know a super-bad guy is going to be somewhere that you can strike and you know you won’t get the opportunity for another year.”

Fontenrose, now at the Atlantic Council, predicted that, while the Iran-backed militias in Iraq might lash out immediately, in revenge for one of their own top commanders killed alongside Suleimani, Tehran would wait and pick the time, place and manner of its retribution – and then strike again and again, possibly for years to come.

“I think they’ll probably try to hit us in other parts of the world, maybe west Africa maybe Latin America to send the message that they could get us anywhere – we should never feel safe. And I think the US is going to kind of try to spread out our assault in a similar way,” she said.

“I don’t think we’re looking at a war. I think we’re looking at a series of asymmetric semi-unpredictable strikes against each other’s interests.”

Play Video 1:37 Aftermath of US airstrike that killed top Iranian general Qassem Suleimani – video report

There are few good reasons to assume that this new raised level of conflict, halfway between cold and hot wars, will be stable, and will not erupt into all-out war. Both sides have a long history of misreading each other’s intentions and overreaching.

And while the consequences of Suleimani’s killing are unclear, what is almost certain is that Trump has not thought them through. He made the decision while on holiday at his Florida resort. He did it without the sombre presidential address to explain his actions to the nation as is customary at such pivotal junctures in the country’s history, merely tweeting out a US flag and leaving it to the Pentagon make the announcement.

Over the past three years, the national security decision-making process, by which the pros and cons of US action were once carefully weighed, has been gutted. There are few high-level policy meetings any more. The independent thinkers in Trump’s orbit have left the stage, leaving a president who ultimately trusts his gut instincts above any expert.

It is those instincts that have, more than any other single factor, led the US and Iran to this point, and in particular Trump’s visceral hatred of his predecessor, Barack Obama, and his diplomatic legacy, the 2015 nuclear deal. Destruction of the deal and the economic strangulation of Iran, became a central imperative of Trumpian foreign policy.

Those aides who remain in the president’s orbit have survived because they know how to echo his impulses, his desire to destroy all traces of Obama, and who now share the president’s focus on his own re-election.

The decision to kill Suleimani is likely to have been made with the November vote in mind – how it might play as a punchline on the campaign trail, finally eclipsing perhaps Obama’s conquest of Osama bin Laden.

But it will be a story that will almost certainly be told against a backdrop of more attacks, greater uncertainty and a deepening sense of dread.

“If this thing sparks into a war, it will absolutely not benefit us,” warned retired Lt Col Daniel Davis, a veteran of Afghanistan and Iraq now at the Defense Priorities thinktank. “It will be catastrophic for everyone.”