On June 9, 1898, the British under Queen Victoria brokered a99-year lease agreementfor the use of Hong Kong after China lost a series of wars fought over the British trade in tea and opium... actually, it was leased.
During the second half of the 19th century, the British had grown increasingly worried about the security of their free port at Hong Kong. It was an isolated island, surrounded by areas still under Chinese control. The British decided the answer would be to lease a buffer zone around Hong Kong that would make the island less vulnerable to invasion.[SUP][citation needed
In 1860, at the end of the Second Opium War, the UK gained a perpetual lease over the Kowloon Peninsula, which is the mainland Chinese area just across the strait from Hong Kong Island. This agreement was part of the Convention of Beijing that ended that conflict.[SUP][citation needed
In 1898, the British and Chinese governments signed the Second Convention of Peking, which included a 99-year lease agreement for the islands surrounding Hong Kong, called the "New Territories". The lease awarded control of more than 200 surrounding small islands to the British. In return, China received a promise that the islands would be returned to it after 99 years, at the end of the single negotiated term of lease.
On 19 December 1984, British Prime Minister Margaret Thatcher and Chinese Premier Zhao Ziyang signed the Sino-British Joint Declaration, in which Britain agreed to return not only the New Territories but also Kowloon and Hong Kong itself when the lease term expired. China promised to implement a "One Country, Two Systems" regime, under which for fifty years Hong Kong citizens could continue to practice capitalism and political freedoms forbidden on the mainland.[SUP][citation needed
Kowloon was a perpetual lease, which is a defacto cede of territory.[/SUP]