The Origins of the Six-Day War, which was fought between June 5 and June 10, 1967, by Israel and the neighboring states of Egypt [known then as the United Arab Republic (UAR)], Jordan, and Syria, lay in both longer term and immediate issues. The foundation of Israel linked to the Palestinian Refugee problem and its participation in the invasion of Egypt during the Suez crisis of 1956 continued to be a significant grievance for the Arab world. Arab nationalists, led by Egyptian President Gamal Abdel Nasser, continued to be hostile to Israel's existence. By the mid-1960s, relations between Israel and its Arab neighbors had deteriorated to the extent that a number of border clashes had taken place. In 1967, Egypt expelled UN peacekeepers stationed in the Sinai Peninsula since the Suez conflic