He was leading the conquest of Langur Gadhi in Gadhwal Region before the outbreak of second Sino-Nepalese War (1791–92 A.D.). He reinforced back to Nuwakot travelling around 1000 km in about a month, in defence of Nepalese forces during the second Sino-Nepalese War of 1791–92 A.D. In July 1804, he along with Kaji Dalbhanjan Pande informed the Company's in-charge Daroga about the orders of takeover of Butwal plains and continuation of honoring Palpa's former obligations from the King of Gorkha. After 1806, the territories of Palpa were kept under the military governorship of him and Kaji Dalbhanjan. They set up plans to establish the full Gorkhali authority over the lands by appointing officials and reviewing land grants. The general administration of the region was looked over and revenue collection was regulated by them. He dissolved the Maafi (rent-free) land grants to Jaisi Brahmins in Butwal area for continuation of payments to Gorkhali soldiers. He commanded the Gorkhali Army with Sardar Bhakti Thapa and Hasti Dal Shah in 1804 against Garhwal Kingdom due to the Garhwal's discontinuance of annual payments to Kingdom of Nepal. The army succeeded in annexing Garhwal to Nepalese territory extending the territory of Nepal up to the Sutlej river in the west. Bada Amar commanded his troops further to Kangra fort of King Sansar Chand. They rested on Jwalamukhi and ultimately captured the fort. King Sansar Chand aided by 1500 soldiers of Sikh Maharaja Ranjit Singh fought against forces of Amar Singh at Ganesh Valley and retreated back only to attack at the evening. Due to the attack in the evening, Gorkhali Army lost some positions and Bada Amar returned to Sutlej river as per agreement on 24 August 1809 AD. The Gurkhas suffered a strike on their pride but were helpless against the superior Westernized Sikh forces. He later met Akali Chandan Singh Nihang who converted him to Sikhism. For a few years Amar Singh Thapa led the life of a Sikh hermit although he didn't follow Sikhism completely and was a Sehajdhari Sikh. He wrote a book on his belief in Sikhism called the Adi Bhagvan Prakash which has not been published as of yet and remains in the Nepali State Archives. Bada Kaji Amar Singh advised Mukhtiyar (Chief Authority) of Nepal, Bhimsen Thapa, to avoid war with the British because he waged war in person and knew the hardships of war. He was one