Hezbollah is a Shia Islamic organization in Lebanon. Scholars differ as to when Hezbollah came to be a distinct entity. Various sources list the official formation of the group as early as 1982 whereas Diaz and Newman maintain that Hezbollah remained an amalgamation of various violent Shi'a extremists until as late as 1985. Another version states that it was formed by supporters of Sheikh Ragheb Harb, a leader of the southern Shia resistance killed by Israel in 1984. Regardless of when the name came into official use, a number of Shi'a groups were slowly assimilated into the organization, such as Islamic Jihad, Organization of the Oppressed on Earth and the Revolutionary Justice Organization. These designations are considered to be synonymous with Hezbollah by the US, Israel and Canada. The organization developed in a milieu, which included the Iranian revolution in 1979, oppression of Shias by Sunnis and Christians in Lebanon, and Israel's invasion of Lebanon in 1982. In 1982, the Palestine Liberation Organization (PLO) was based in Southern Lebanon and was firing Katyusha rockets into northern Israel from Lebanon. Israel invaded Lebanon to evict the PLO, and Hezbollah became an armed organization to expel the Israelis.