Iranian involvement in the Iraq War

The 2003 invasion of Iraq, which toppled Iraqi president Saddam Hussein and his Arab Socialist Ba'ath Party, was the decisive event that allowed Iran to begin exerting an unprecedented level of influence on Iraqi politics. Leveraging the fact that Shia Muslims account for the majority of the population in both countries, the Iranian government used Shia militias to serve Iran's interests during the Iraq War. This culminated in Iran's involvement in the Iraqi insurgency, in which there were instances of Shia militants engaging the Multi-National Force in direct combat. Organizations that enjoyed large-scale Iranian support included the Mahdi Army of Muqtada al-Sadr, as well as Kata'ib Hezbollah, Asa'ib Ahl al-Haq, and the Promised Day Brigade. Since 2007, the United States has employed a "kill or capture" strategy with regard to confronting Iranian operatives in the Iraqi conflict.