Complex sentence: The British arrived in Assam in the year 1826 as per Yandaboo Accord and since then they selected Dibrugarh as a centre of Administration as well as for business purpose in Upper Assam, and Dibrugarh turned into a hub in this region of North-Eastern India.
Split into simpler sentences: The British arrived in Assam in the year 1826 as per Yandaboo Accord. They selected Dibrugarh as an administrative and commercial center in Upper Assam making Dibrugarh a hub of activity in this region of North-Eastern India.