River systems of Thailand divides into two major branches, the " Tiền Giang" (Front River) and "Hậu Giang" (Back River). These in turn enter the South China Sea through nine estuaries. The following are the principal tributaries of Mekong River which flow through Thailand (tributaries entirely outside the Thai border not shown). The Mekong drains a considerable portion of northeast Thailand. In terms of Thai territory drained, it is second only to the Chao Phraya system. The Salawin River rises in Tibet (Tibetan: རྒྱལ་མོ་རྔུལ་ཆུ།) after which it flows through Yunnan, where it is known as the "Nujiang" River (), although either name can be
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