Yemen is an ancient country. In the millennia before Christianity, the two Yemens, known as South Arabia and Arabia Felix ("Happy Arabia"), were important points along the incense trade routes. South Arabian kingdoms dating from 1000 B.C. included the land from which the Queen of Sheba made her visit to King Solomon. Prior to the coming of Islam in the sixth century A.D., the South Arabian kingdoms declined, the conquests of Persian and Ethiopian rulers failed, and the famous dam at Ma'rib was destroyed. Remnants of the dam and pillars, reputedly from the queen's temple, are still to be found in the eastern desert of Yemen. Leadership under the Zaydi imams began in the ninth century. Between the eleventh and fourteenth centuries, various external and local dynasties struggled for power in different parts of Yemen. Among these were the Sulayhid (including the noted queen, Arwa), Ayyubid, and Tehirid dynasties. Yemen resisted foreign rule, but two occupations by the Ottoman Turks occurred—between the mid-sixteenth to early seventeenth centuries and from the 1870s to 1918. The imams then sought to reassert their political authority over the tribes of Yemen and against Saudi Arabia. The assassination of Iman Yahya in 1948 was eventually followed by a successful revolt of dissident army officers, intellectuals, and businessmen in 1962. Civil warfare lasted into the 1970s and reerupted in the 1990s.