Phibun's alliance with Japan during the early years of war was initially popular. The Royal Thai Army joined Japan's Burma campaign with the goal of recovering their historical claims to part of the Shan states, previously surrendered to the Burmese Empire in the Burmese–Siamese wars and subsequently annexed by the British following the Third Anglo-Burmese War. They gained the return of the four northernmost Malay states lost in the Anglo-Siamese Treaty of 1909, and with Japanese mediation in the Franco–Thai war they also recovered territory lost in the Franco-Siamese War of 1893.