Yemen was one of the oldest centers of civilization in the Near East. Between the 12th century BC and the 6th century AD, it was part of the Minaean, Sabaean, and Himyarite kingdoms, which controlled the lucrative spice trade, and later came under Ethiopian and Persian rule.
In the 7th century, Islamic caliphs began to exert control over the area. After this caliphate broke up, the former north Yemen came under control of Imams of various dynasties usually of the Zaidi sect, who established a theocratic political structure that survived until modern times
Egyptian Sunni caliphs occupied much of north Yemen throughout the 11th century. By the 16th century and again in the 19th century, north Yemen was part of the Ottoman Empire, and in some periods its Imams exerted control over south Yemen.
The modern history of Yemen began in 1918 when North Yemen gained independence from the Ottoman Empire. North Yemen became a republic in 1962, but it was not until 1967 that the British Empire, which had set up a protective area around the southern port of Aden in the 19th century, withdrew from what became South Yemen. In 1970, the southern government adopted a Communist governmental system. The two countries were formally united as the Republic of Yemen on May 22, 1990.