Historically the border region has been a contested area located at the edge of the various Indian and Burmese empires. Britain had begun conquering India in the 17th century, and gradually took control of most of the country, forming British India. From the 1820s-80s Britain also gradually conquered Burma; by the Treaty of Yandabo in 1826 which ended the First Anglo-Burmese War Burma recognised British control over Assam, Manipur, Rakhine (Arakan), and the Taninthayi coast, thereby delimiting much of the modern boundary in general terms. In 1834 the Kabaw Valley areas was returned to Burma and a modified boundary delimited in this region, dubbed the 'Pemberton line' after a British commissioner, which was later refined in 1881. In 1837 the Patkai Hills were unilaterally designated as the northern boundary. Large swathes of Burma were annexed following the Second Anglo-Burmese War of 1852–53. The remainder of Burma was conquered in 1885 and incorporated into British India. In 1894 a boundary between Manipur and the Chin Hills was delimited, and the existing 'Pemberton line' boundary modified again in 1896. Further boundary modifications were made in 1901, 1921 and 1922.