Stone tools, weapons, elephants, and remnants of large stone structures provide evidence that Bhutan was inhabited as early as 2000 BC, although there are no existing records from that time. Historians have theorised that the state of Lhomon (lit. 'southern darkness'), or Monyul ("Dark Land", a reference to the Monpa, an ethnic group in Bhutan and Arunachal Pradesh, India), may have existed between 500 BC and AD 600. The names Lhomon Tsendenjong (Sandalwood Country) and Lhomon Khashi or Southern Mon (country of four approaches), have been found in ancient Bhutanese and Tibetan chronicles.[32][33] The dzong in the Paro valley, built in 1646 Buddhism was first introduced to Bhutan in the mid of 7th century AD. The Tibetan king Songtsen Gampo[34] (reigned 627–649), a Buddhist convert, extended the Tibetan Empire into Sikkim and Bhutan.[35] He ordered the construction of two Buddhist temples, Jambay Lhakhang in Bumthang in central Bhutan and Kyichu Lhakhang in Paro Valley.[36] Buddhism was propagated in earnest[34] in 746[37] under King Sindhu Rāja (also Künjom;[38] Sendha Gyab; Chakhar Gyalpo), an exiled Indian king who had established a government in Bumthang at Chakhar Gutho Palace.[39]: 35 [40]: 13  The Portuguese cannons in the National museum of Paro Trashigang Dzong, built in 1659 By the 10th century, Bhutan's religious history had a significant impact on its political development. Various subsects of Buddhism emerged that were patronised by the various Mongol warlords.[41] Bhutan may have been influenced by the Yuan dynasty with which it shares various cultural and religious similarities.[42] After the decline of the Yuan dynasty in the 14th century, these subsects vied with each other for supremacy in the political and religious landscape, eventually leading to the ascendancy of the Drukpa Lineage by the 16th century.[36][43] Sketch of Bhutan's interior, 1783 Painting of Bhutan, 1813 British envoys in Bhutan's royal court in 1905 A thrikhep (throne cover) from the 19th century. Throne covers were placed atop the temple cushions used by high lamas. The central circular swirling symbol is the gankyil in its mode as the "Four Joys". Locally, Bhutan has been known by many names. The earliest Western record of Bhutan, the 1627 Relação of the Portuguese Jesuits Estêvão Cacella and João Cabral,[44] records its name variously as Cambirasi (among the Koch Biharis[45]), Potente, and Mon (an endonym for southern Tibet).[29] Until the early 17th century, Bhutan existed as a patchwork of minor warring fiefdoms, when the area was unified by the Tibetan lama and military leader Ngawang Namgyal, who had fled religious persecution in Tibet. To defend the country against intermittent Tibetan forays, Namgyal built a network of impregnable dzongs or fortresses, and promulgated the Tsa Yig, a code of law that helped to bring local lords under centralised control. Many such dzong still exist and are active centres of religion and district administration. Portuguese Jesuits Estêvão Cacella and João Cabral were the first recorded Europeans to visit Bhutan in 1627,[46] on their way to Tibet. They met Zhabdrung Ngawang Namgyal, presented him with firearms, gunpowder and a telescope, and offered him their services in the war against Tibet, but the Zhabdrung declined the offer. After a stay of nearly eight months Cacella wrote a long letter from the Chagri Monastery reporting on his travels. This is a rare extant report of the Zhabdrung.[47][48] When Ngawang Namgyal died in 1651, his death was kept secret for 54 years. After a period of consolidation, Bhutan lapsed into internal conflict. In 1711, Bhutan went to war against the Raja of the kingdom of Koch Bihar in the south. During the chaos that followed, the Tibetans unsuccessfully attacked Bhutan in 1714.[49] This period was marked by an increase in Bhutan's influence in Koch Bihar.[50] In the 18th century, the Bhutanese invaded and occupied the kingdom of Koch Bihar. In 1772, the Maharaja of Koch Bihar appealed to the British East India Company which assisted by ousting the Bhutanese and later attacking Bhutan itself in 1774. A peace treaty was signed in which Bhutan agreed to retreat to its pre-1730 borders. However, the peace was tenuous, and border skirmishes with the British were to continue for the next hundred years. The skirmishes eventually led to the Duar War (1864–65), a confrontation to control of the Bengal Duars. After Bhutan lost the war, the Treaty of Sinchula was signed between British India and Bhutan. As part of the war reparations, the Duars were ceded to the United Kingdom in exchange for a rent of ₹50,000. The treaty ended all hostilities between British India and Bhutan. During the 1870s, power struggles between the rival valleys of Paro and Tongsa led to civil war in Bhutan, eventually leading to the ascendancy of Ugyen Wangchuck, the penlop (governor) of Trongsa. From his power base in central Bhutan, Ugyen Wangchuck defeated his political enemies and united the country following several civil wars and rebellions during 1882–85.[51] In 1907, an epochal year for the country, Ugyen Wangchuck was unanimously chosen as the hereditary king of the country by the Lhengye Tshog of leading Buddhist monks, government officials, and heads of important families, with the firm petition made by Gongzim Ugyen Dorji. John Claude White, British Political Agent in Bhutan, took photographs of the ceremony.[52] The British government promptly recognized the new monarchy. In 1910, Bhutan signed the Treaty of Punakha, a subsidiary alliance that gave the British control of Bhutan's foreign affairs and meant that Bhutan was treated as an Indian princely state. This had little real effect, given Bhutan's historical reticence, and also did not appear to affect Bhutan's traditional relations with Tibet. After the new Union of India gained independence from the United Kingdom on 15 August 1947, Bhutan became one of the first countries to recognise India's independence. On 8 August 1949, a treaty similar to that of 1910, in which Britain had gained power over Bhutan's foreign relations, was signed with the newly independent India.[32] In 1953, King Jigme Dorji Wangchuck established the country's legislature—a 130-member National Assembly—to promote a more democratic form of governance. In 1965, he set up a Royal Advisory Council, and in 1968 he formed a Cabinet. In 1971, Bhutan was admitted to the United Nations, having held observer status for three years. In July 1972, Jigme Singye Wangchuck ascended to the throne at the age of sixteen after the death of his father, Dorji Wangchuck.