On March 14, 1978, in what is known as “Operation Litani,” Israeli forces invade Southern Lebanon to combat PLO militants based there. The UN reacts immediately, issuing resolution 425, insisting that Israel withdraw its troops and allow the UN to place interim forces there. UN forces arrive in Lebanon on March 23. Israel, however, does not remove all of its troops from Lebanon until June of that year. In 1982, Israel re-invades Lebanon, leaving again in May of 2000.