Britain occupies the island of Hong Kong in January 1841 as a result of the First Opium War and takes formal possession of the Island on January 26, 1841 raising the Union Jack at Possession Point. China went on to formally cede the Island of Hong Kong to the British under the Treaty of Nanking (or Nanjing), signed on August 29, 1842, formally making it a British colony.
The treaty was followed 56 years later in 1898 by a 99-year lease that allowed Britain to control even more land with the lease ending in 1997.