The war was, in many ways, inevitable. Neither Israel nor her Arab neighbours were satisfied with the outcome of the 1948 conflict. Israel had been left with borders that were difficult to defend, her citizens vulnerable to attacks from all sides. The Arabs had never supported the Partition Plan, and having failed to abort Israel at the outset, began planning for the day when they could eradicate the Jewish state.
Relations between Israel and Syria had been dismal for years. The two countries has sparred over control of water from the Jordan River, and Israel held the Ba’ath regime responsible for terrorist attacks perpetrated by militants operating from Syria.
Syria, anticipating an Israeli response to the border violations, signed a defence agreement with Egypt. According to the agreement, signed on 4 November 1966, an armed attack against either of the two signatories would be considered an armed attack against both. And, once war erupted, the Syrian and Egyptian armies were to operate jointly under the command of the Egyptian chief of staff.
In 1967, Egypt began to turn up the heat. On May 16, Egypt ordered UNEF troops to evacuate the Sinai region (U Thant agreed, without consulting either the UN General Assembly or Security Council, and much to Nasser's delight, also pulled troops out of Gaza). Thousands of Egyptian troops, 80,000 men and 600 tanks in less than three days, poured into the area and began to entrench themselves. Israel turned to both the US and the United Nations for assistance. Both suggested 'patience'; the Security Council was all but deadlocked by the Soviets and France. Fearing they were becoming politically isolated, Israel’s response was to begin to call up reserves--18,000 men on May 17, and an additional 17,000 the following day.
But it was Nasser's decision to close the Straits of Tiran that was the defining moment. Most countries, including the US, considered the closure to be a casus belli, an action tantamount to an Act of War. Israel required the Strait to reach Eilat, at the time it's most important port. And the Arabs also increased the vitriol of their rhetoric: Syria's Foreign Minister Ibrahim Makhous declared that “the withdrawal of the UN forces means ‘make way, our forces are on their way to battle.’” According to then-Defense Minister Hafez el-Assad, the Syrian army had “its finger on the trigger and demand[ed] that the battle be expedited.” 1.
Again, Israel pleaded with the US to intercede, but America was unwilling to challenge the Soviets, which were sponsoring the Arab states (and according to recent historical documents, had been lying to the Arabs telling them that Israel was preparing for war). 2.
Nevertheless, Nasser knew full well that closing the Straits would force Israel into war. After only a few weeks, Israel was running low on oil and food. Then France refused to honour previously signed agreements for planes and parts. Egypt continued the provocation: We are now’, Nasser declared, ‘on the verge of a confrontation with Israel’....‘If’, he added ominously, ‘the Jews threaten us war? I say to them “Welcome”, we are ready for war!'
With everyone still suggesting patience, time was running out. Both Egypt and Syria continued to amass troops and build defences. Israeli hospitals began to collect blood. Emergency morgues were prepared. Israel's military leaders now advised a preemptive strike: “Whoever waits for the Egyptians to start the war has got to know that we’ll lose the land of Israel!” Moshe Dayan declared, “It’s lunacy to wait!” The final straw was an intelligence report that Egypt was moving its army from a defensive to an offensive position, apparently with the intention of occupying Eilat.
After weeks of exhaustive efforts to forestall war, the Cabinet voted in favour of a preemptive strike. The attack would begin early the next morning, Monday, June 5.
1. Theodore Draper, Israel and World Politics: Roots of the Third Arab-Israeli War, p. 60.