Arab nationalists led by Egyptian President Gamal Abdel Nasser refused to recognize Israel, and called for its destruction. By 1966, Israeli-Arab relations had deteriorated to the point of actual battles taking place between Israeli and Arab forces. In May 1967, Egypt massed its army near the border with Israel, expelled UN peacekeepers, stationed in the Sinai Peninsula since 1957, and blocked Israel's access to the Red Sea. Other Arab states mobilized their forces.
Israel reiterated that these actions were a casus belli. On 5 June 1967, Israel launched a pre-emptive strike against Egypt. Jordan, Syria and Iraq responded and attacked Israel. In a Six-Day War, Israel defeated Jordan and captured the West Bank, defeated Egypt and captured the Gaza Strip and Sinai Peninsula, and defeated Syria and captured the Golan Heights. Jerusalem's boundaries were enlarged, incorporating East Jerusalem, and the 1949 Green Line became the administrative boundary between Israel and the occupied territories.
Following the 1967 war and the "three nos" resolution of the Arab League, during the 1967–1970 War of Attrition Israel faced attacks from the Egyptians in the Sinai, and from Palestinian groups targeting Israelis in the occupied territories, in Israel proper, and around the world. Most important among the various Palestinian and Arab groups was the Palestinian Liberation Organization (PLO), established in 1964, which initially committed itself to "armed struggle as the only way to liberate the homeland". In the late 1960s and early 1970s, Palestinian groups launched a wave of attacks against Israeli and Jewish targets around the world, including a massacre of Israeli athletes at the 1972 Summer Olympics in Munich. The Israeli government responded with an assassination campaign against the organizers of the massacre, a bombing and a raid on the PLO headquarters in Lebanon.
On 6 October 1973, as Jews were observing Yom Kippur, the Egyptian and Syrian armies launched a surprise attack against Israeli forces in the Sinai Peninsula and Golan Heights, that opened the Yom Kippur War. The war ended on 26 October with Israel successfully repelling Egyptian and Syrian forces but having suffered over 2,500 soldiers killed in a war which collectively took 10–35,000 lives in just 20 days. An internal inquiry exonerated the government of responsibility for failures before and during the war, but public anger forced Prime Minister Golda Meir to resign.
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