Nasser's popularity in Egypt and the Arab world skyrocketed after his nationalization of the Suez Canal Company and his political victory in the subsequent Suez Crisis. Calls for pan-Arab unity under his leadership increased, culminating with the formation of the United Arab Republic with Syria from 1958 to 1961. In 1962, Nasser began a series of major socialist measures and modernization reforms in Egypt. Despite setbacks to his pan-Arabist cause, by 1963 Nasser's supporters gained power in several Arab countries, but he became embroiled in the North Yemen Civil War and eventually the much larger Arab Cold War. He began his second presidential term in March 1965 after his political opponents were banned from running. Following Egypt's defeat by Israel in the 1967 Six-Day War, Nasser resigned, but he returned to office after popular demonstrations called for his reinstatement. By 1968, Nasser had appointed himself Prime Minister, launched the War of Attrition to regain lost territory, began a process of depoliticizing the military and issued a set of political liberalization reforms. After the conclusion of the 1970 Arab League summit, Nasser suffered a heart attack and died. His funeral in Cairo drew five million mourners and an outpouring of grief across the Arab world.