The Six-Day War (Hebrew: מִלְחֶמֶת שֵׁשֶׁת הַיָּמִים, Milhemet Sheshet HaYamim; Arabic: لنكسة, an-Naksah, “The Setback” or حرب 1967, Ḥarb 1967, “War of 1967”), also known as the June War, 1967 Arab–Israeli War, or Third Arab–Israeli War, was fought between 5 and 10 June 1967 between Israel and Jordan, Syria, and Egypt.
Relations between Israel and its neighbours were not normalised after the 1948 Arab–Israeli War. In 1956 Israel invaded the Sinai peninsula in Egypt, with one of its objectives being the reopening of the Straits of Tiran that Egypt had blocked to Israeli shipping since 1950. Israel was eventually forced to withdraw, but was guaranteed that the Straits of Tiran would remain open. A United Nations Emergency Force (UNEF) was deployed along the border, but there was no demilitarisation agreement.
In the months prior to June 1967, tensions became dangerously heightened. Israel reiterated its post-1956 position that the closure of the Straits of Tiran to Israeli shipping would be a cause for war (a casus belli). Egyptian President Gamal Abdel Nasser announced in May that the Straits would be closed to Israeli vessels, and then mobilised Egyptian forces along the border with Israel, ejecting UNEF. On 5 June, Israel launched a series of airstrikes against Egyptian airfields, initially claiming that it had been attacked by Egypt, but later stating that the airstrikes were preemptive. The question of which side caused the war is one of a number of controversies relating to the conflict.
The Egyptians were caught by surprise, and nearly the entire Egyptian Air Force was destroyed with few Israeli losses, giving the Israelis air supremacy. Simultaneously, the Israelis launched a ground offensive into the Gaza Strip and the Sinai, which again caught the Egyptians by surprise. After some initial resistance, Nasser ordered the evacuation of the Sinai. Israeli forces rushed westward in pursuit of the Egyptians, inflicted heavy losses, and conquered the Sinai Peninsula.
Jordan had entered into a defence pact with Egypt a week before the war began; the agreement envisaged that in the event of war Jordan would not take an offensive role but would attempt to tie down Israeli forces to prevent them making territorial gains. About an hour after the Israeli air attack, the Egyptian commander of the Jordanian army was ordered by Cairo to begin attacks on Israel; in the initially confused situation, the Jordanians were told that Egypt had repelled the Israeli air strikes.
Egypt and Jordan agreed to a ceasefire on 8 June, and Syria agreed on 9 June; a ceasefire was signed with Israel on 11 June. In the aftermath of the war, Israel had crippled the Egyptian, Syrian and Jordanian militaries, having killed over 20,000 troops while losing fewer than 1,000 of its own. The Israeli success was the result of a well-prepared and enacted strategy, the poor leadership of the Arab states, and their poor military leadership and strategy. Israel seized the Gaza Strip and the Sinai Peninsula from Egypt, the West Bank, including East Jerusalem, from Jordan and the Golan Heights from Syria. Israel’s international standing greatly improved in the following years. Its victory humiliated Egypt, Jordan and Syria, leading Nasser to resign in shame; he was later reinstated after protests in Egypt against his resignation. The speed and ease of Israel’s victory would later lead to a dangerous overconfidence within the ranks of the Israel Defense Forces (IDF), contributing to initial Arab successes in the subsequent 1973 Yom Kippur War, although ultimately Israeli forces were successful and defeated the Arab militaries. The displacement of civilian populations resulting from the war would have long-term consequences, as 280,000 to 325,000 Palestinians fled or were expelled from the West Bank and over 100,000 fled from the Golan Heights. Across the Arab world, Jewish minority communities fled or were expelled, with refugees going mainly to Israel. (Source)