Relations soured once again in 1979, as Saddam Hussein formally took office and the Shah of Iran was overthrown in the Islamic Revolution and replaced by a Shi'ite theocracy under Ayatollah Ruhollah Khomeini. War broke out in 1980 when Iraq invaded Iran, leading to the eight-year long Iran-Iraq War. Almost the entire ground war was fought in close proximity to the international boundary, though the conflict resulted in stalemate and following the end of fighting no changes to the border were made. Relations were restored in 1990 and have improved substantially since the overthrow of Saddam Hussein in 2003.