The Iranian Revolutionary Guard Corps (IRGC) has long exerted a strong, often underestimated power in the Middle East. With around 190,000 members, plus an estimated 450,000 reserves in the Basij paramilitary, the largest component of Iran’s Armed Forces also controls much of the country’s politics, intelligence and economy.

After an Israeli airstrike assassinated the Islamic Republic’s Supreme Leader Ayatollah Ali Khamenei on February 28, US President Donald Trump called on the IRGC to lay down its arms in exchange for immunity. IRGC forces refused the offer, and with many more of its leaders killed over the last month, it shows no sign of giving up.

As US ground forces deploy to the Middle East, it is imperative to understand that – despite a month of widespread US-Israeli bombing, damaged infrastructure, internal fractures and decimated leadership – the IRGC will likely resist any invasion of Iranian territory with tenacity. Its history demonstrates why.

Read more: Trump underestimated Iran’s resilience. Now there is only one way out of the war

From militia to frontline force

The IRGC originally emerged in the 1979 revolution from the ad hoc street militias made up of students loyal to Ayatollah Ruhollah Khomeini’s vision of an Islamic Republic. It was opposed to the factions that sought to create a secular republic after the overthrow of the monarchy, and sought to be a national guard to protect the nascent Islamic revolutionary government.

Also known as the Pasdaran-e Enghelab, “Guardians of the Revolution”, it soon evolved into a praetorian guard for the country’s supreme leader.

In the force’s earliest days it prevented a counter-revolution by the Artesh, the standing military under the Shah. The IRGC also fought street battles with rival revolutionary forces, including secular leftists and rival Islamist militias.

With Iraq’s invasion of Iran in 1980, the IRGC emerged as a frontline conventional combat force in tandem with........

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