The Yemen Civil War could have been a local power struggle, if not for the Saudis' heavy hand.
Yemen is a small, poor country in a region empires have plundered for centuries. This civil war is a local struggle that has been escalated out of control by the ambitions of powers outside of Yemen—mainly Saudi Arabia.
The British Empire ruled the Yemeni city of Aden in South Yemen as a colony, a refueling station for ships on the way to the Empire's Indian possessions. Gaining independence in 1967, South Yemen had a socialist government from 1970 on, becoming the People's Democratic Republic of Yemen (PDRY).
Northern Yemen was ruled by a king from the city of Sana'a who followed of the Zaydi denomination of Islam, clashing periodically with both the British and with the Saudi kingdom over borders in the 1930s. Arab nationalist revolutionaries overthrew the king in 1962, starting a civil war between nationalists, backed by Arab nationalist (Nasserite) Egypt and royalists, backed by Saudi Arabia, Jordan, and Iran (then a monarchy too). A peace deal was reached and by 1970, even Saudi Arabia recognized North Yemen as the Yemen Arab Republic (YAR).
North and South Yemen talked about unification throughout the 1970s and '80s, and it finally happened in 1990, after the fall of the Soviet Union that had been South Yemen's most important ally.
Ali Abdullah Saleh, who was killed this December 3, was a military man who had been president of North Yemen since he was appointed by a junta in 1978. He became president of the unified country in 1990.