There were three Burmese invasions of Assam between 1817 and 1826, during which time the Kingdom of Assam (Ahom) came under the control of Burma from 1821 to 1825.
Locally, this period, called the “manor din” by the Assamese and Chahi-Taret Khumtakpa (seven years of devastation) in Manipuri, is remembered with horror.
It was the climactic period of the 600-year history of the Assamese kingdom. The sharp drop in population due both to depredations as well emigrations left the erstwhile kingdom in shambles. The British, who were earlier reluctant to colonise Assam, came into direct contact with a belligerent Burmese occupying force.
The Kingdom of Assam came under the control of Burma during this period after more than 100 years of peace under the Sahom Dynasty. The local people still call these years of devastation and it was the most revolutionary phase of Assamese history. Britishers were formally unwilling to colonize Assam but post the Anglo Burmese war they annexed Assam as well as Burma.
A lot of fighting and killing took place between the years during which, the Burmese monarchs of Mandalay tried to suppress the Shan Ahom Assamese kingdom. Maha Tihlawa who was a garrison commander specifically committed a lot of atrocities along with his troops. The native hill tribes also started looting the cities and killing a lot of people.
Population of Assam was reduced drastically and almost 1/3rd of its people were killed. The Burmese invasion and ancillary events weakened the state of Assam to such a degree that in the year 1839 the kingdom was totally annexed by British Raj.