In the years following the 1958 Iraqi revolution, the United States enjoyed friendly, if sometimes tense, relationships with Egypt, Israel, Saudi Arabia, Kuwait, Jordan, Lebanon, Tunisia and Morocco. U.S.-Egyptian relations cooled, however, following President Nasserís 1962 deployment of Egyptian troops to Yemen to fight Saudi-supported royalists. The U.S. in turn aided their Saudi allies, a critical oil source.
In Israel: The Embattled Ally, Nadav Safran notes that Egyptian involvement in the Yemen war also impacted relations with the Americans vis-a-vis the question of Israel. As Egypt built up its military capabilities during the Yemen war, the Israelis approached the Americans for weapons and diplomatic assistance. U.S. military aid to Israel had been negligible, but in 1963 the Americans approved the transfer of Hawk surface-to-air missiles to Israel and recommitted to Israelís security and the need to maintain a regional balance of power. By 1965, under the leadership of President Lyndon B. Johnson, the United States cut its economic assistance to Egypt, and U.S.-Egypt relations reached a nadir, pushing the Egyptians closing to the Soviets. The Soviets exploited the Arab-Israeli conflict and American "imperialism" to promote pro-Soviet Arab unity, turning the region in an arena for a proxy power struggle between the USSR and the Americans.
The Americansí role in the 1967 war was also influenced by its earlier involvement in the 1956 Suez Canal crisis. President Dwight Eisenhower pressured Israel to withdraw from Sharm el-Sheikh despite the fact that the Egyptians did not offer any concessions in return. Significantly, though, Eisenhower did pledge that the U.S. would guarantee Israelís right of passage in the Straits of Tiran. The Americans also sponsored a United Nations resolution establishing the United Nations Emergency Force presence between the Egyptians and the Israelis.
During the run up to the Six-Day War, the Americans repeatedly rebuffed Israeli requests for military aid and approval for an Israeli preemptive attack on Egypt. The United States, bogged down in Vietnam and facing domestic opposition to that war, was loathe to become embroiled in a second front. Rather than get involved militarily, the Americans aggressively pursued diplomatic solutions and sought to cobble together an international regatta to challenge the Egyptian blockade on Israeli shipping in the Straits of Tiran, a campaign that ultimately failed. But while the U.S. continued to refuse to aid Israel militarily, the American opposition to unilateral Israeli action began to soften in the beginning of June 1967.
Six Days of War: June 1967 and the Making of the Modern Middle East, Michael B. Oren, 2002