The Lebanese Civil War (1975–1990) was a conflict that became greatly worse by Lebanon's changing demographics. There was conflict between Sunnis and Shias, between Christians and Muslims, and the involvement of Syria, Israel and the Palestine Liberation Organization (PLO). After a short break in the fighting in 1976 due to Arab League mediation and Syrian intervention, civil strife continued, with fighting primarily focused in south Lebanon, occupied first by the PLO, then occupied by Israel. On May 17, 1983, a US-backed agreement was reached for making peace between Lebanon and Israel. The agreement failed when Syria refused to withdraw its forces.