persecution in Tibet. To defend the country against intermittent Tibetan forays, Namgyal built a network of impregnable dzong (fortresses), and promulgated the Tsa Yig, a code of law that helped to bring local lords under centralized control. Many such dzong still exist and are active centers of religion and district administration. Portuguese Jesuits Estêvão Cacella and João Cabral were the first recorded Europeans to visit Bhutan, on their way to Tibet. They met Ngawang Namgyal, presented him with firearms, gunpowder and a telescope, and offered him their services in the war against Tibet, but the Shabdrung 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 Shabdrung. After Ngawang Namgyal's death in 1651, his passing was kept secret for 54 years; after a period of consolidation, Bhutan lapsed into internal conflict. In the year 1711 Bhutan went to war against the Mughal Empire and its Subedars, who restored Koch Bihar in the south. During the chaos that followed, the Tibetans unsuccessfully attacked Bhutan in 1714.
In the 18th century, the Bhutanese invaded and occupied the kingdom of Cooch Behar to the south. In 1772, Cooch Behar appealed to the British East India Company which assisted them in ousting the Bhutanese and later in 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 for 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 Rs. 50,000. The treaty ended all hostilities between British India and Bhutan
