Israel had been in a pretty constant state of war with its Arab neighbours since its formation in 1948. A brief history of the Arab-Israeli conflict prior to the Yom Kippur War -
  • 1948 Arab-Israeli War: An attempt by the Arab states to make Israel "cease to exist" because they refused to accept its formation out of part of Palestine. The invaders were repelled.
  • Suez Crisis,1956: The two main aims of the Suez War were to stop Arab terrorism against Israeli citizens and to recapture the Suez canal after the Egyptians nationalized it. It actually wasn't a crisis for Israel, which achieved its objective.
  • The Six Day War: Israel launched a pre-emptive strike against Egypt as they geared up for an invasion themselves, and then Jordan and Syria opened hostilities against Israel. This is the war that led to the capture of the West Bank and the Gaza Strip by Israel.

So far Israel had done pretty well for itself. In the Six Day War it had also captured the Sinai Peninsula. It decided that it now had a good geographic strategic depth from its neighbours to be relatively safe. As well as this, Israeli intelligence did not indicate that an attack was likely during the festival of Yom Kippur, especially as in the year of the war (1973), it also fell in the month of Ramadan. They were wrong.

Egypt and Syria wanted to capture back land of theirs that was under Israeli occupation (Sinai and the Golan Heights respectively). On October 6, 1973 they launched surprise attacks in these areas. The Syrians were repelled in the north but managed to make some breakthroughs in the south of the Golan Heights, advancing into Israeli-occupied territory. Israeli Defence Forces reserve troops arrived to replace the destroyed defenders, and managed to push Syrian forces back to the initial border by October 11. They then proceded into Syria and began heavy shelling of Damascus. The United Nations arranged a cease fire on this front, with an agreement to return to pre-war borders.

Egypt was successful initially as well, advancing 15 kilometres over the Suez canal into Sinai. However, they had not anticipated this success and had no contingency for what to do next. Their thinly spread forces were easily smashed from October 16 onwards, and by October 26 international pressure from the USSR and USA led to a cease-fire on the Egyptian front.

Israel actually lost territory because of the war, as it abandoned the west bank of the Suez canal to the Egyptians and a small strip of land on the western coast of Sinai. In 1974 Syria and Israel signed a disengagement agreement leaving Syria with a small part of the Golan Heights. This was the first sign of Israeli weakness and territorial loss since its formation. UN stations were placed in both areas to monitor the agreements.