Hong Kong is an island in the Pearl River Delta, in Southern China. British forces occupied the island in the First Opium war of 1839-42, and it became a formal overseas possession with the 1842 Treaty of Nanking. In 1860 and 1898, the territory of the colony was expanded beyond the original island, and a 99 year lease was signed to negotiate the return of the colony to China eventually. In December 1941 the Japanese Empire invaded and occupied the colony until 1945, whereupon British sovereignty was restored. The local population grew in the 1950s formed by expatriates from the communist revolution in China, and in 1984 a join Sino-British Agreement paved the way for a return to Chinese rule in 1997. Since then Hong Kong remains a Special Administrative Region of China and an important global finance centre.