The war began when Iraq invaded Iran, launching a simultaneous invasion by air and land into Iranian territory on 22 September 1980 following a long history of border disputes, and fears of Shia Islam insurgency among Iraq's long-suppressed Shia majority influenced by the Iranian Revolution. Iraq was also aiming to replace Iran as the dominant Persian Gulf state. Although Iraq hoped to take advantage of the revolutionary chaos in Iran (see Iranian Revolution, 1979) and attacked without formal warning, they made only limited progress into Iran and were quickly repelled by the Iranians who regained virtually all lost territory by June 1982. For the next six years, Iran was on the offensive.