When Israel attacked the Sinai airfields on 5 June 1967, it enjoyed more than the advantage of total surprise. Israeli commanders knew that the Egyptian army was already engaged in a full-scale conflict in the Yemen. Any power would be overstretched trying to fight two wars at the same time. Egypt had neither the logistical means nor the surplus wealth to engage a foe like Israel while pinned down in South Arabia. Egypt's five-year war in Yemen had severely sapped its war preparedness in advance of the third Arab-Israeli war. Although we could not claim that Egypt lost the 1967 War in Yemen – there were too many other variables behind Israel's swift victory – there is no doubt that Egypt's campaign in Yemen fatally impaired its performance in the war against Israel.

Egypt entered the Yemeni civil war in September 1962, almost immediately after the officers’ coup that overthrew the monarchy of Imam Badr. Despite some second thoughts, Gamal Abdel Nasser gave his full support to the revolutionary movement as part of his new policy of promoting progressive Arab forces over reactionary regimes. The initial Egyptian military deployment was limited, and Nasser's aides, with Anwar Sadat at the forefront, assured him that a short mission by a small force would be more than enough to ensure victory. Instead, the Egyptians found themselves embroiled in an increasingly complex conflict that divided Arab ranks and drew South Arabia into the superpower rivalries of the Cold War. In the aftermath of the dissolution of Egypt's union with Syria, Nasser was in no position to accept another failure in his Arab nationalist policies. There was no clear point when the Egyptians could declare mission accomplished and withdraw from Yemen without loss of prestige. In this sense, Yemen proved an unwinnable war, Nasser's Vietnam.