On 26th June 1843 the Treaty of Nanking, 南京條約, signed between British and Chinese governments after the First Opium War, came into effect, as part of the treaty the island of Hong Kong is ceded to the British ‘in perpetuity’.
Formally called the Treaty of Peace, Friendship and Commerce between Her Majesty the Queen of Great Britain and Ireland and the Emperor of China, it was originally signed on 29th August he previous year in 1842 to mark the end of the Opium War. It was the first in a line of unequal treaties against the Chinese, as the British had no obligations to fill in return.
The treaty consisted on 13 articles including the cessation of Hong Kong and to open several Chinese ports to British trade. Hong Kong was ceded back to the Chinese only in 1997.