By launching a hugely successful preemptive strike that crippled the Egyptian Air Force. Israel dedicated 95% of its air force to the attack on Egyptian airfields, and the success of this attack allowed Israel to divert large portions of its air power to the Jordanian and Syrian fronts as well, giving Israel a huge advantage on the ground, which culminated in successful Israeli advances into the Sinai Peninsula, the Golan Heights, and the West Bank.

Also, Israel's vulnerability lie in more than just numbers. At its narrowest, there were only nine miles between the West Bank and the Mediterranean, meaning a successful push by Jordan could divide the country in two. In the month leading up the Six-Day War, it became increasingly clear that Israel faced imminent attack. Egypt sent multiple brigades into the Sinai Peninsula, ordered the UN peacekeepers stationed there to withdraw (which they did), and closed the Straits of Tiran to Israel, dealing a severe economic blow. Syria's military had been under Egyptian control since 1966, but in late May of 1967, Jordan and Iraq also agreed to unify their forces with Egypt's. Rhetoric from the leaders of Egypt, Syria, and Jordan was explicit in its warmongering. Taking into account Israel's many obvious disadvantages, Israeli leaders determined a preemptive strike was their only option.

Six Days of War, Michael B. Oren