Ancient Yemen was the center of two advanced civilizations—the Minaean kingdom, which some scholars date back to as early as 1200 B.C., and the Sabaean kingdom, which arose in the 700's B.C. Through control of the incense and spice trade routes that passed through their land, the Sabaeans grew rich and powerful and eventually reduced the Minaean kingdom to a vassal state. The kingdoms of Qataban and Hadhramaut on the south Arabian coast also came under Sabaean control. The Himyarites, a local tribe, replaced the Sabaeans as the dominant power in the region in the second century B.C.

In the sixth century A.D., the declining Himyarite kingdom was conquered first by the Ethiopians and then by the Persians. By the time of the Prophet Mohammed's death in 632, Yemen had been won to Islam by conversion and force of arms. During the ninth century, the Zaidis migrated from Mesopotamia to the Yemen highlands. The Zaidi leader, the imam, later brought the Shafi tribes along the coast under his rule.

In 1517 Yemen was conquered by the Ottoman Turks. Ottoman rule, however, was frequently nominal, and at times the imam achieved autonomy. In much of Yemen, especially in the southern part, petty sheikhs and sultans—who owed allegiance only to the imam—ruled.

Great Britain occupied the port of Aden on the southern coast in 1839 and by 1914 had signed treaties of protection with the rulers of all the neighboring sheikhdoms and sultanates. Aden became a separate British colony and the other areas were administered loosely as the Aden Protectorate (later called Protectorate of South Arabia).

The defeat of the Ottoman Empire in World War I brought independence to the imamate. Imam Yahya fought to extend the boundaries of his domain north and south, clashing with the Saudi Arabians and the British. Conflict was ended in 1934 with the signing of two treaties—the Treaty of Taif with Saudi Arabia and the Treaty of Sana with Great Britain.

In 1948 Imam Yahya was assassinated by a rival claimant to the throne. Yahya's son, Ahmad, won control of the imamate.

During 1958–61, Yemen and Egypt were nominally federated. In 1962 Ahmad died and he was succeeded by his son, Badr. Within a week, army leaders deposed Badr and set up the Yemen Arab Republic. Civil war broke out, with Egypt supporting the republicans with troops and military supplies and Saudi Arabia backing the royalists (the supporters of the imam) with military supplies. In 1967 Egypt withdrew its forces and in 1970 Saudi Arabia ended its aid to the royalists. A new republican government was then formed that included some royalists.

Meanwhile in the Aden Protectorate, the British in 1963 united the various sheikhdoms and sultanates into a loose confederation, called the Federation of South Arabia. However, in the years that followed most of the sheikhs and sultans were overthrown by Marxist rebels, and in 1967 Great Britain granted the region independence. A Marxist regime came to power and named the country Southern Yemen. In 1970, the country was renamed the People's Democratic Republic of Yemen. It was popularly called Yemen (Aden), while the Yemen Arab Republic was called Yemen (Sana).

Beginning in the 1970's Yemen (Aden) repeatedly attacked Yemen (Sana) in an attempt to win control of the country. Following a severe clash between armies of the two Yemens, the nations entered into negotiations on creating a union. During the 1980's, despite occasional attacks by groups from Yemen (Aden) across the border into Yemen (Sana), the negotiations continued.

Meanwhile, in 1986 civil war in Yemen (Aden) erupted between two factions. After a week of fighting, in which some 13,000 persons died, the more radical faction gained control but continued the country's commitment to the negotiations with Yemen (Sana).

During the late 1980's both countries made their governments more democratic, and the Yemen (Aden) regime modified its Marxist principles to permit more free enterprise in preparation for union with Yemen (Sana). In 1990 the two nations united to form the Republic of Yemen. Sana was designated the capital. Many in the south resented the union, and in 1994 a rebellion broke out and a separate state was set up in the south. After a two-month civil war the north defeated the rebels.

In 1999, Yemen held its first election in which the president was elected directly by the people. Ali Abdullah Salih, who had served as president of the Republic of Yemen since 1990, won the election and continued as president. He was reelected in 2006.

However, civil and political violence continued in Yemen. In the south, protests and demonstrations against the Salih government began in 2007. A rebellion in the far north erupted in 2004. A truce was agreed upon in 2008, but violence returned and later became open warfare in 2009.