After the Gurkhas had established their hold over Garhwal and Kumaon, their borders came directly in touch with those of the British territory in Gorakhpur and elsewhere. They began to raid territory controlled by the British and this forced Lord Hastings to take the decision to declare war. It was decided to attack Nepal simultaneously from as many points a possible. 

As a result, Maj. Gen. Merley was sent with a force of eight thousand men to Bihar with orders to directly march to Kathmandu, while Maj. Gen. Wood was sent at the head of a four thousand strong force to Gorakhpur. These campaigns do not directly have a bearing on the history of Garhwal. 

Gen. Gillespie was sent with three thousand five hundred men to enter  Garhwal  through  the  Dun  valley  and  dislodge  Amar  Singh Thapa from Srinagar. He found the Gurkhas firmly entrenched at Fort Kalanga, to the east of Dehradun. After an attempt to storm the fort failed, siege was laid to the fort on 26th October, 1813. 

Many unsuccessful assaults were launched. These were gallantly resisted by the Gurkhas. The General himself brought up the reserves but was killed. At last, it was discovered that there was no water in the fort and the garrison was compelled to resort to a spring at some distance. This was cut off and the fire from the batteries resumed the next day, doing great damage to the fort and its gallant defenders. On the night of 30th  November, Balbhadra Thapa, with the surviving seventy  men, evacuated the fort and escaped to a neighbouring hill where he was joined by about 300 other Gurkhas who were waiting to find their way into the besieged fort. This regrouped force was confronted by Maj. Ludlow but they escaped to the Jauntgarh fort, where it successfully withstood a siege by a British force.

In the meanwhile, after razing Kalanga to the ground, Col. Carpenter joined the forces under Gen. Martindell and they occupied Nahan. A third Gurkha force led by Amar Singh Thapa opposed Gen. Ochterlony on the banks of the Satluj river. He skillfully forced them to evacuate their strong posts and concentrate at Malaun.

Thus, the present campaign remained inconclusive and this made Lord Hastings more anxious to gain a foothold in the Kumaon hills.