Why does the American Legion use 1982-84 for eligibility in membership, yet most applications under OPM uses dates of hostilities for Lebanon as June 1983-1987? Israeli invasion and international intervention: 1982–84Main article: 1982 Lebanon WarAfter continued PLO-Israeli exchanges, Israel invaded Lebanon on June 6 in Operation Peace for Galilee. By June 15, Israeli units were entrenched outside Beirut and Yassir Arafat attempted through negotiations to evacuate the PLO. It is estimated[by whom?] that during the entire campaign, approximately 20,000 were killed on all sides, including many civilians[citation needed]. A multinational force composed of U.S. Marines, French, Italian units arrived to ensure the departure of the PLO and protect defenseless civilians. Nearly 15,000 Palestinian militants were evacuated by September 1.President Bashir Gemayel agreed to send troops from his Phalange militia into camps to clear out 2,000 PLO fighters. On September 14, Gemayel was assassinated. Phalangists entered the camps on September 16 at 6:00 PM and remained until the morning of September 19, massacring 700–800 Palestinians, according to official Israeli statistics, "none apparently members of any PLO unit".[9] These are known as the Sabra and Shatila massacres. It is believed that the Phalangists considered it retaliation for Gemayel's assassination and for the Damour massacre which PLO fighters had committed earlier in a Christian town.[10]Amine Gemayel succeeded his brother and focused on securing the withdrawal of Israeli and Syrian forces. A May 17, 1983, agreement among Lebanon, Israel, and the United States arranged an Israeli withdrawal conditional on the departure of Syrian troops. Syria opposed the agreement and declined to discuss the withdrawal of its troops, effectively stalemating further progress.In 1983 the IDF withdrew southward, and would remain only in the "security zone" until the year 2000. Explosion at the Marine barracks seen from afarIntense attacks against U.S. and Western interests, including two truck bombings of the US Embassy in 1983 and 1984 and the landmark attacks on the U.S. Marine and French parachute regiment barracks on October 23, 1983, led to an American withdrawal, while the virtual collapse of the Lebanese Army in February 1984 was a major blow to the government. On March 5 the Lebanese Government canceled the May 17 agreement and the Marines departed a few weeks later.