What are the causes of the Arab-Israeli War of 1967 or Six-Day War?
Answer 1 - Listing
There are numerous causes to this conflict and the list below is not exhaustive.
1) "Wipe Israel off the Map" Statements: Arab Nationalists, especially Charismatic Egyptian President Gamal Abdel Nasser of Egypt, were pushing strongly for Israel's elimination and made daily speeches about how the Arab States were going to invade and remove Israel from the map to form a unified Arab State. He began to coordinate military strategy with Syria and Jordan (to a lesser degree) as to how to invade Israel effectively. These threats were made daily and consistently in 1967. Additional troops were added to the Egyptian Army and that army began to be arrayed closer and closer to the Israeli border.
2) Removal of UNEF Forces: As a condition of the Israeli withdrawal from the Sinai Peninsula in 1956, the UN deployed security forces to the Sinai Peninsula to prevent Egypt from massing troops in the Sinai. Nasser evicted the UNEF (the UN security force) from the Sinai Peninsula in contravention of the Armistice for the 1956 Suez Crisis and placed large numbers of Egyptian soldiers and armored divisions on the Israeli-Egyptian border.
3) Arab Military Coordination: Nasser coordinated military strategy quite closely with Syria and Jordan. It was clear to many at the time that these forces would not sit idle for long. A number of Syrian battalions were positioning themselves in the Golan Heights above the Sea of Galilee and Jordanian positions in the West Bank were becoming more entrenched.
4) Closure of Waterways: Egypt, counter to the armistice ending the 1956 War, closed the Suez Canal to Israeli shipping and then proceeded to close the Straits of Tiran to Israeli shipping, cutting Israel off from trade with Iran which was Israel's greatest ally in the Middle East at the time and primary supplier of petroleum. This had the effect of strangling Israel and is considered by Israel to be the primary causus belli.
5) Best Defense is a Good Offense: Israel realized that its borders were too close to for them to risk an Arab Invasion of Israel before retaliating. Israel would have to fight a pre-emptive war in order to secure the best probability of success in a military engagement. The first act of open warfare was when Israel destroyed 2/3 of the Egyptian Air Force on the tar mac on June 5, 1967.
6) Imperialist Israel: (Written by someone else) It's when Israel wanted to occupy "their" land, and decided to attack their neighboring Arab countries for it.
Answer 2 - Discussion
The Six-Day War had a number of proximate and chronic causes.
Chronic Causes: Israel and the Arab States were only in Armistice for 18 years and during that time Arab Nationalism really developed. One of its cornerstones was Pan-Arab Unity and a non-Arab State (like Israel) that divided Arabs from each other (not to mention the Palestinian Exodus) was a wedge in that dream. Therefore, Egyptian President Gamal Abdel Nasser repeatedly threatened to push Israel "into the sea." Israel was also very jumpy in the sense that they had little in the way of international protection (as the United States did not become a strong backer of Israel until after the Six-Day War) and very indefensible borders.
Proximate Causes: Egypt made a number of overt threats to the peace and security of Israel. They closed the Straits of Tiran to Israeli Shipping which cut off Israel from Iran (who at that time was ruled by the Shah and in Alliance with Israel) and other South Asian Nations. This severely diminished Israel's ability to procure petroleum. Also the armies of Egypt, Syria and Jordan mobilized their troops to surround Israel and kicked out the UN observers who had been maintaining the Armistice.
Between the fear of a slow death (because of the lack of
petroleum) and the fear of a quick death (because of the mobilized
armies on its borders) Israel decided that a surprise attack was
the best way to deal with these threats. Israel never expected the
attack to be the overwhelming success that it was.