Onetime allies, the United States and Iran have seen tensions escalate repeatedly in the four decades since the Islamic Revolution.

In March 2003, U.S. forces invaded Iraq vowing to destroy Iraqi weapons of mass destruction (WMD) and end the dictatorial rule of Saddam Hussein. When WMD intelligence proved illusory and a violent insurgency arose, the war lost public support. Saddam was captured, tried, and hanged and democratic elections were held. In the years since, there have been over 4,700 U.S. and allied troop deaths, and more than one hundred thousand Iraqi civilians have been killed. Meanwhile, questions linger over Iraq's fractious political situation.