China has one of the oldest continuous civilizations, with records dating back about 3,500 years. Successive dynasties developed a system of bureaucratic control that gave the agrarian-based Chinese an advantage over neighboring nomadic and hill cultures. Chinese civilization was further strengthened by the development of a Confucian state ideology and a common written language that bridged the gaps among the country's many local languages and dialects. Whenever China was conquered by nomadic tribes, as it was by the Mongols in the 13th century, the conquerors would adopt the ways of the underlying civilization and staff the bureaucracy with local Chinese. The last imperial dynasty was established in 1644, when the Manchus overthrew the Ming dynasty and established the Qing (Ch'ing) dynasty with Beijing as its capital. At great expense in blood and treasure, the Manchus over the next half century gained control of many border areas, including Xinjiang, Yunnan, Tibet, Mongolia, and Taiwan. The success of the early Qing period was based on the combination of Manchu martial prowess and traditional Chinese bureaucratic skills. During the 19th century, Qing control weakened and prosperity diminished. China suffered massive social strife, economic stagnation, explosive population growth, and Western mercantile influence. The Taiping and Nian rebellions, along with a separatist movement in Xinjiang, drained Chinese resources and almost toppled the dynasty. Britain's desire to continue its illegal opium trade with China collided with imperial edicts prohibiting the drug, and the so-called First Opium War erupted in 1840. After China lost the war, Britain and other Western powers, including the United States, occupied "concessions" and gained special commercial privileges. Hong Kong was ceded to Britain in 1842 under the Treaty of Nanking, and in 1898, when the opium wars finally ended, Britain received a 99-year lease of the new territories, significantly expanding the size of the Hong Kong colony.