A (very simplified) timeline of US intervention in the middle-east.
Iran democratically elected a secular leader, but he wanted to use iranian oil for iran. So the CIA instead helped the Shah into dictatorial power, who would sell the drilling rights to american and british companies. He opressed his populace so bad, that they turned to Ayatollah Khomeni and his religious extremists to get rid of him. The religious zealots have been in power ever since.
To fight against the Ayatollah Regime that drove out western oil companies, the US illegally bypasses a weapons embargo to arm a neighbouring dictator called Saddam Hussein. He wages the first Gulf War on Iran for 8 years, which results in ~750.000 dead. The poison gas attacks happen with the knowledge of the US.
Russia invades Afghanistan, the US arms local resistance fighters, a group called Al Quaeda under one Osama bin Laden. To help the islamists against the godless Russians, thousands of mercenaries and religious extremists from muslim countries are recruited by the CIA and brought to Afghanistan, they become the Taliban. More than a million civillians die.
Saddam Hussein, seeing no win against Iran instead invades the absolutist, slavetrading monarchy of Kuwait. Kuwait had opened it oil-wells to western companies, so with the help of the CIA and an american PR-agency, the daughter of Kuwaiti ambassador pretends to be a nurse and lies about Iraqi soldiers ripping babies out of incubators. The world is shocked. What follows is the second Gulf War. More than a million dead civillians again.
Following this second gulf war, american troops are stationed in the gulf region protecting “western values” (the oil wells). The religious extremists in Afghanistan are not amused, the sheer existence of nonbelievers on holy ground is blasphemy to them. Al Quaeda (formerly funded by the US and the House of Saud) begin their campaign against the west.
Following September 11 2001 the US invades first Afghanistan, then Iraq and don’t really bother with the long-term stabilizing of a region they so effectively destabilized. From the chaos rises the Islamic State.