Hong Kong[e] is a special administrative region of the People's Republic of China. With 7.4 million residents of various nationalities[f] in a 1,104-square-kilometre (426 sq mi) territory, Hong Kong is the fourth most densely populated region in the world. Hong Kong was established as a colony of the British Empire after the Qing dynasty ceded Hong Kong Island in 1841–1842 as a consequence of losing the First Opium War. The colony expanded to the Kowloon Peninsula in 1860 and was further extended when the United Kingdom obtained a 99-year lease of the New Territories in 1898. Hong Kong was occupied by Japan from 1941 to 1945 during World War II. The territory was handed over from the United Kingdom to China in 1997. Hong Kong maintains separate governing and economic systems from that of mainland China under the principle of one country, two systems.[g]