In the years before the Six Day War, Egypt was ruled by Gamal Abdel Nasser, who in 1952, as a lieutenant colonel in the Egyptian army, had helped lead the overthrow of the monarch, King Farouk, by the so-called “Free Officers’ Movement.” Nasser had named himself prime minister in 1954, and in 1956 had promulgated a constitution which would establish Egypt as a one party “socialist state,” with Islam as the official religion. Standing as the sole candidate for election as president, Nasser had won with 99.948 percent of the vote, while his constitution had garnered 99.8 percent of the vote.
Nasser began his rule as a pan-Arabist, with plans to unify the Arab states into a single entity under his command, and as a reformer, who wanted to modernize the country and fight endemic corruption, all within the context of one-party dictatorial rule.
While a founder of the so-called “Non-Aligned Movement” with India and Yugoslavia, Egypt under Nasser developed close relations with the Soviet Bloc. The Soviet Union and its satellites became Nasser's chief source of military equipment and financial aid, beginning with a massive arms deal with Czechoslovakia in 1955.
Nasser soon began to have conflicts with other Arab countries, especially Saudi Arabia and Jordan, which opposed his aspirations to lead the Arab world. There were multiple attempts by Egyptian intelligence to assassinate Jordan’s King Hussein, and in 1962 Egypt intervened in Yemen against royalists backed by Saudi Arabia. Expecting an easy victory, Egyptian forces instead got bogged down in a guerilla war. Nasser responded by attempting to subvert Saudi Arabia itself and by attacking supposed Yemeni royalist bases in Saudi Arabia. The attacks against Jordan and Saudi Arabia caused a marked deterioration in US-Egyptian relations and also harmed Nasser’s reputation in the Arab world.
In 1964, Israel completed its National Water Carrier, a series of canals and pipelines to transport water from the relatively water-rich northern part of the country to the much dryer southern regions. This project promised to allow increased population growth and immigration, and also to spur industrial and agricultural development, and was therefore strenuously opposed by the Arab countries.
Syria, by now led by a Ba’athist regime hostile to Nasser, took the lead in demanding Arab action to destroy the Israeli water project. It condemned Egypt, the largest Arab country, for not attacking Israel and for “hiding behind the skirts” of the UN peacekeeping force that stood between Egypt and Israel.
Nasser, however, did not believe at the time that the Arabs were unified enough to defeat Israel, and he chose to defer a confrontation until what he saw as a more propitious moment.
In May of 1967, Nasser expelled UN peacekeepers from the Sinai peninsula and announced a blockade of the Straits of Tiran to Israel-bound shipping. The blockade sealed off the major Israeli port of Eilat and violated the armistice agreements that had followed the 1956 Sinai war. It was regarded by most observers as a casus belli, or act of war. These bold — and in retrospect reckless — moves provoked massive pro-Nasser street demonstrations in Arab capitals, and one after another Arab government endorsed Nasser's steps and put its military under direct Egyptian control. Even Jordan’s King Hussein did so. In addition, the Soviet Union encouraged the Arab states in their militancy.
Open warfare had seemed a distant possibility before May, but now everything had changed. Nasser had engineered the Arab unity that he had judged necessary to confront Israel, he had openly declared that the time had come to destroy the Jewish state, and he had taken steps that constituted acts of war.