The Anglo-Siamese Treaty of 1909 was a treaty between the United Kingdom and the Kingdom of Siam that effectively defined the modern borders between Thailand and British-controlled territories in Malaysia. Through this treaty, Siam ceded control of some territories (including the states of Kedah, Kelantan, Perlis, and Terengganu) to British control. However, it also formalized British recognition of Siamese sovereignty over the territories that remained, thus largely securing Siam's independent status. The treaty helped establish Siam as a "buffer state" between French-controlled Indochina and British-controlled Malaya. This allowed Siam to retain its independence while neighboring countries were colonized.