The Babai River originates in and completely drains Inner Terai Dang Valley of Mid-Western Nepal. Dang is an oval valley between the Mahabharat Range and Siwalik Hills in its eponymous district. Dang was anciently home to indigenous Tharu people and came to be ruled from India by the House of Tulsipur who also counted as one of the Baise Rajya —a confederation of 22 petty kingdoms in the Karnali (Ghagra) region. About 1760 AD all these kingdoms were annexed by the Shah Dynasty during the unification of Nepal, except Tulsipur lands south of the Siwalik Hills were not taken. Since Dang Valley was somewhat higher, cooler, better-drained and therefore less malarial than most of the country's Inner Terai, it was settled to some extent by Shah and Rana courtiers and other Paharis long before DDT was introduced to control the disease-bearing Anopheles mosquito.