Hong Kong.

“After the First Opium War (1839–42), Hong Kong became a British colony with the perpetual cession of Hong Kong Island, followed by the Kowloon Peninsula in 1860 and a 99-year lease of the New Territories from 1898. Hong Kong was later occupied by Japan during World War II until British control resumed in 1945. In the early 1980s, negotiations between the United Kingdom and China resulted in the 1984 Sino-British Joint Declaration, which paved way for the transfer of sovereignty of Hong Kong in 1997, when it became a special administrative region (SAR) with a high degree of autonomy.”