Salween River much of its length, the Salween's course is nearly parallel to that of the much larger Mekong in the east. Although the commonly accepted name is Salween, the river is known by a handful of other names regionally: "Nu" in China, "Thanlwin" in southern Burma, and "Salawin" on the border of Thailand and Burma. Several major sub-continental drainage basins border on the Salween. The Mekong basin forms nearly the entire eastern boundary of the watershed, while the Irrawaddy River flows southwards on the west side of the basin. The smallest boundary is formed by the Yangtze to the extreme north.
Burma Railway and 250,000 Southeast Asian civilian labourers ("rōmusha") and about 61,000 Allied prisoners of war were subjected to forced labour during its construction. About 90,000 civilian labourers and more than 12,000 Allied prisoners died. A railway route between Burma and Thailand, crossing Three Pagodas Pass and following the valley of the Kwhae Noi river in Thailand, had been surveyed by the British government of Burma as early as 1885, but the proposed course of the line – through hilly jungle terrain divided by many rivers – was considered too difficult to undertake. In early 1942, Japanese forces invaded Burma and seized