Yemeni unification took place on May 22, 1990, when the area of the People's Democratic Republic of Yemen (also known as South Yemen) was united with the Yemen Arab Republic (also known as North Yemen), forming the Republic of Yemen (known as simply Yemen).
Unlike East and West Germany, Communist and Nationalist China, North and South Korea, or North and South Vietnam, the two Yemens were not formed by a civil war or occupation. North Yemen became a state after the collapse of the Ottoman Empire in November 1918, whereas South Yemen at that time had been administered as part of British India, and was then a British colony in its own right. In one of the many proxy conflicts of the Cold War, a South Yemeni insurgency (with the support and backing of the Soviet Union) led by two nationalist parties revolted, causing the United Kingdom to withdraw from its former colony.
Following the North Yemen Civil War, the north established a republican government that included tribal representatives. It enjoyed modest oil revenues and remittances from its citizens working in the oil-rich Arab states of the Persian Gulf. Its population in the 1980s was estimated at 12 million as opposed to 3 million in South Yemen.