The Old City of Jerusalem during the Six-Day War, June 1967, Getty Images. June 5 marks the beginning of the Six- Day War. Relations between Israel and its neighbours had never fully normalised following the 1948 Arab-Israeli War. Israel reiterated its 1950s statement that the closure of the Straits of Tiran for its ships would be a casus belli (case for war). But in late May, Egyptian President Gamal Abdel Nasser announced that he would close the straits to Israeli vessels, then mobilised its forces along its border with Israel. Israel launched a preemptive strike against Egypt's air force, beginning the war.