Iran has been promoting a terrorist campaign against the U.S. since the 1980s.
Iran used this network of emissaries to fight Saddam Hussein, and to punish Saudi Arabia and the USA for their support in Iraq. In the Iraq War, Iran operated a terrorist organization that included four Shia militias and two militias. This is in order to prevent the US from establishing a forward base from which to operate militarily against Tehran. Many signs indicate that the USA under the Biden administration will not deviate from its policy, and will not strike at Iran.