The Abors immigrated to their Indian homeland from the north crossing the Himalayas into the Assam Valley. Eventually they retreated into the highland regions that they Currently occupy. The cause of this migration is unknown, although natural causes and political upheaval have been suggested as possible catalysts. It is also not known whether they migrated as a solid body at a single point in history, or in smaller subgroups over a period of several hundred years. Between 1847 and 1862, the British government tried unsuccessfully to conquer all of Abor territory. Following the failure of several military endeavors, a treaty was reached that guaranteed limited British hegemony and uninhibited trade and communication on the frontier. In spite of occasional treaty violations, an uneasy peace was maintained. After the final British military action against the Abor (in response to the murder of the assistant political officer and a companion) in 1912, the hills north of Assam were divided into western, central, and eastern sections for administrative purposes. The last of these were collectively given the name of Sadiya Frontier Tract. In 1948, the Tirap Frontier Tract was divided into the Mishmi Hills District and the Abor Hills District. Finally, in 1954, the name of the Abor Hills District was changed to the Siang Frontier Division. Since this time, the Abor have undergone considerable acculturation, which has resulted in a number of changes in the nature of village life, the local economy, social structure, and political organization.