From Citizendium, the Citizens' Compendium
In 1839 Bhutan was convulsed with civil war. British government in India complained to the Deb of Bhutan that the Raikat of Byakantapur had taken over the possession of western Duars and that Bhutan government was not strong enough to settle even the problems of its own country. The British demanded compensation for this. On Bhutan’s denial, British governor Auckland on September 6, 1841, ordered the occupation of Assam Duar on payment of 10,000 rupees annually to Bhutan.
There was tension in Bengal as well about the ownership of land. In the following years, Bhutan and India attempted to solve the issue but failed.
In 1852, Bhutanese docoits robbed the British territory. In its response, British India stopped the payment of part of the annual tribute owed to Bhutan. To settle the case, Dewangiri Dzongpon, uncle of Shabdrung, deputed an envoy to Calcutta. The mission failed to find a solution.
An agent of Assam reported to the Governor General that the Bhutanese had kidnapped Uttam Chand, an Indian citizen. British India fined 7000 rupees to Dewangiri Dzongpon and Trongsa Penlop. The second Assam Infantry also demanded 14000 rupees as a fine, punishment to the offender and the retrocession of all the properties that Bhutanese had confiscated from Assam.
Bhutanese Deb replied with 2,808 rupees as compensation and apologizing for all Bhutanese that were involved in such activities.
On such situation, a British India’s spy, the hereditary Zamindar of Gooman Duar sought asylum in British territory. Bhutan demanded his extradition but the British did not acquiesce. Then a Bhutanese armed group entered British territory through Bhulka Pass, kidnapped Arun Singh and other spies from Assam, and fled back to Bhutan. Two more similar incidents occurred in Mainaguri and Cooch Behar. During 1856-57, Bhutanese offenders seeking shelter under British protection were forcefully taken by the Bhutanese from Assam Duars. In 1859 the Bengal government submitted a list of 33 cases of alleged aggression in the previous two years in which 45 people had been carried off, and Colonel Jenkins was authorized to take over Ambaree Fallacotah.
Plans for settlement
When the dispute in the border areas increased, Governor General sent an envoy comprising the Lieutenant of Bengal Sir F. Haillday, Assam Colonel Jenkins and others to Bhutan, but their efforts were in vain. Bhutan neglected the envoy.
The British react
By that time, the British had opened their military post at Jalpaiguree; the 11th Military Group with the 73rd Native Infantry were assembled there. Halliday was given the charge of the military post. When Halliday reported to Governor General that a little encouragement could raise the people of Assam Duars against Bhutan, the Governor General ordered him to do so. He gathered all the armies who were fighting against the Sepoy Mutiny in Ambari Falakata and Jalpaish and sent them to Bhutan.
On the other hand ,in 1862, under Dalimkot Dzongpon’s orders, the Bhutanese kidnapped 13 villagers and 23 cowherds from Ambari Falakata. Some 300-400 Bhutanese entered Cooch Behar, confiscated 123 buffalos, two shepherds, six watermen, and an estimated amount of 20,936 rupees. When, after that, British India captured Ambari Falakata, the Bhutanese tended to credit off the treasure stolen from Sikkim and Cooch Behar.
Ashley Eden Mission
To conclude the outrages of the Duars, British India planned to dispatch yet another mission to Bhutan. The mission aimed not only to settle the outstanding problem of the Duars but also to study the military strength of Bhutan. They were to study the situation of Bhutan so that it would be easy to spy out the feasibility for the future military arrangement. They concluded that the only way was to force Bhutan to accept the mission in the court of Deb.
Civil war was going on in Bhutan at that time headed by Trongsa Penlop, Jigme Namgyal. When the Deb received the news of mission approaching to his court, he said that the mission was not convenient at that time. But no problem, what Bhutan say British organised a mission under the leadership of Ashley Eden to sent to Bhutan in 1862.
The mission deputed from Calcutta in August 1863 for Bhutan. Eden was given with a draft treaty to be finalised after a discussion with Lhengye Tshog, a doll of Trongsa Penlop. The terms of the treaty were:
Ambari Falakata would be returned when the Bhutanese return the British property and captives;
The government of Bhutan would inquire into the outrages committed by British and Cooch Behar subjects and give redress;
The government of Bhutan would surrender all the British and Bhutanese subjects accused of crimes within British India with the assurances that the British government would in return surrender all Bhutanese subjects accused of crimes in Bhutan;
The Bhutan government would seek the advices of British government over disputes with the Rajahs of Sikkim and Cooch Behar because these were British-protected areas;
Bhutan government would receive a British agent in Bhutan; and
Free trade and commerce should be established between the two countries.
The mission with difficulty reached Punakha but could not reach any agreement with the Bhutanese government. Bhutan demanded more compensation and return of the Bhutanese offenders taking asylum in India. India denied such demanded.
The mission was manhandled and mistreated. Trongsa Penlop drafted another treaty and forced Eden to sign. Tactically, Eden signed and wrote "under compulsion" under it as no Bhutanese could read English. Seeing his life in danger, Eden escaped back to India and declared the treaty as invalid.
The mission returned to Darjeling by the end of April 1864. Eden, for the humiliation of the British mission, shared his view with Fort William and suggested permanent or temporary occupation of the country and destruction of all Bhutanese forts, or permanent occupation of Assam and Bengal Duars.
British then planned for the war. They assembled military troops at Assam, Bengal and Cooch Behar areas. The force was divided into two groups and four branches. The eastern group was headed by General Dunsford and the western group by General Mulcaster. A far eastern column was to start from Gauhati to Dewangiri (Deothang), and the central eastern was to enter through Goalpara to Bishenshing (present day Gelephu). The central western group was to approach to Buxa and Balla (near Phuentsholing), and the far western group would proceed from Jalpaiguree to Chumurchi (Samtse) and Kalimpong. Having this prepared military force, British India declared war against Bhutan on November 12, 1864.
On December 2, ethe astern group crossed Brahmaputra and settled at Gauhati. Three companies of the Assam Light Infantry captured Dewangiri on December 10. The compensation of Ambari Falakata and Assam Duars were already withheld. British India then annexed Bengal and Assam Duars and so much of hill territory including the parts of Dalimkot, Pasakha (Buxa) and Dewangiri as was necessary to command the passes. Having success over these areas, British India opened a military battalion at Bengal. By this time the western group had captured Daling and Mainaguri Duars.
However, on December 16, Shabdrung issued a proclamation, which accused the British of unprovoked aggression against Bhutan. He announced that the Bhutanese people should be ready to resist the attacks of the British and claimed that the British seemed determined to take away the freedom that the Bhutanese had enjoyed for centuries.
As British had captured these areas with some ease, they felt that they could disband their main force and left only one or two armed posts in the new territory and went for resting. Taking this advantage, Bhutan suddenly attacked and captured Dewangiri on January 29, 1865. They had already captured Bishensing, Buxa and Balla on January 25, 26 and 27, with the force led by Trongsa Penlop.
British tried to resist but failed because they had underestimated the Bhutanese determination and misjudged their military strength. In Chumurchi, the force under the command of Trongsa Penlop hardly aggregated 5000 men, nearly half its constituted fighting men which include 1500 Khampa mercenaries. Yet, it threw out gear full two columns of British force of over 12,000 men and six mountain train guns captured, which is now kept at the national museum.
Reoccupation of Dewangiri
In early March 1865 several British commanders were replaced. Brigadier General Frazer Tytler replaced General Dunsford and Brigadier General Tombs replaced General Mulcaster.
When the new commanders had had sudden attacks, the Bhutanese had to surrender at Dewangiri. There, British Indian soldiers imprisoned 120 Bhutanese militias. However, no records have been found about the loss of properties and the number of people who died in the war.
On March 15, Tytler succeeded in capturing Balla without difficulties. The stock of Tazagon was exposed to fire; the Bhutanese lost 44 men and the British lost six men whereas 16 men were wounded.
A historian of Duar observes that though Bhutan had frequent civil war among themselves, they were well organised to resist the incursion of foreign countries.
Dewangiri is the terminus of five passes – Balades, Gurunggaon, Darranga, Libra and Subhankhatta. So, the British had full sight over it for capture. Tomb's force easily captured the stock of Balades. On March 17, a column of 800 infantry and four guns drove the Bhutanese from Darranga and on March 21, the passes of Libra and Gurungaon were examined.
On April 1, 1000 men were sent to Dewangiri, where there were three stockades at a distance of 120 to 150 yards. The British opened fire on the central house and the Bhutanese fled. Most of them died inside the house; 120 surrendered before the British and were killed. “Non was given quarters, the ruthless auxiliaries assuaged their thirst for blood admist the cries for mercy,” records a historian of the Duar War. With these disgraceful scenes, the British re-occupied Dewangiri. This recapture of Dewangiri led the end of the Duar War.
Treaty of Sinchula
The treaty of Sinchula was signed between the Government of Bhutan and British India at Sinchila, India on November 11, 1865. It was also called the Ten Article Treaty of Rawa Rani. In this treaty, the Bhutan government agreed to cede the Assam and Bengal Duars to the British government and to surrender all the subjects of Sikkim and Cooch Behar to the British. Mutual extradition of criminals and establishment of free trade between the two countries were agreed upon. The British government agreed to pay 25,000 rupees for the fulfilment of the terms of treaty - 35,000 rupees on January 10 as the first payment, 45,000 rupees on January 15 on the following year, and 50,000 rupees on January 10 every year following. As the result of the treaty, 2,750 square miles (7,122 square km) of the total land of Bhutan was ceded to British India. Bhutan also lost Ambari Falakata and some of the hill territory on the bank of the Teesta River. In reciprocal basis the treaty secured the exemption of the levy of duty on goods imported to Bhutan territories. It also subjected the attribution of British government to all its disputes over Sikkim and Cooch Behar.
The Sinchula Treaty between the Government of Bhutan and British India has special components, which is also the base of the Indo-Bhutan Treaty of 1949. Articles that are included in the Sinchila Treaty are still working as a milestone to the relation between Bhutan and India.