The home of the ancient kingdom of Sheba from 950 to 115 BC , Yemen was part of the Ottoman Empire from 1517 until the end of World War I. However, Ottoman power in Yemen was always limited, and in reality, the province was ruled by the Zaidi (a branch of Shi'a Islam) imams (religious leaders) who had established the Rassid dynasty in the ninth century. The last of the imams were overthrown in the early 1960s.
In 1839, British forces, who had established their presence in the area as early as 1799, occupied the strategic port of Aden and its surrounding countryside. While the Aden Colony was administered by the British, the rest of Yemen remained under Ottoman/Zaidi control until 1918 when it became an independent kingdom ruled by the Zaidi imams. The imams' position, however, was challenged in 1962 and the dynasty was overthrown, resulting in a civil war between the promonarchy forces supported by Saudi Arabia and the republican forces supported by Egypt. The republican forces established the Yemen Arab Republic (commonly known as North Yemen) in San'a, which was recognized by the super-powers and admitted to the United Nations (UN) in 1963. The Yemeni civil war, however, continued until 1969.
Upon the withdrawal of British forces from the Aden Colony in 1967, Marxist elements took over and established an independent state known as the People's Republic of Southern Yemen. The name was later changed to the People's Democratic Republic of Yemen (PDRY—commonly known as South Yemen). For the most part, relations between the conservative and pro-West government in the north and the Marxist pro-Soviet government in the south were troublesome, culminating in numerous military clashes, including a full-scale war in September 1970 and attempts to overthrow each other's regimes. In June 1978, for example, the North Yemeni president was assassinated when a bomb carried in the briefcase of a South Yemeni envoy exploded. North Yemen accused Aden of involvement in the assassination and fighting broke out between the two countries.
Despite their differences, however, the two Yemens engaged in unity talks as early as 1972. Plans for a unified Yemen were originally drawn up in the mid-1980s, but a 1986 coup in South Yemen and the subsequent civil war postponed reunification. In 1989, the two countries announced that they would merge on 30 November 1990. On 22 May 1990, however, six months ahead of schedule, the Parliaments of the two countries approved the plan for unification and the two Yemens formally merged to form the Republic of Yemen.
On the same day, the Parliaments of the two countries elected Ali Abdullah Saleh, president of North Yemen, as the president of the newly established Republic of Yemen. Ali Salim al-Baid, the former secretary general of the ruling Yemen Socialist Party of South Yemen, was elected as his vice president.