Declining of forest land: large areas of forest land and wasteland were occupied by immigrants for settlement and cultivation. Declining of forest land areas and settlement of immigrant has posed a serious threat to the wildlife and biodiversity of Assam.

1. Immigration during pre-British period: at an early stage, Mongoloid and Austro-Mongoloid people

were come to Assam. Simultaneously, Aryan people came from northern and Eastern India to this region. Sukapha established the Ahom dynasty in Assam. He also came to Assam after crossing the Patkai Mountains. All groups of people inhabiting in Assam have come from different places at different times of history.

2. Immigration during British Rule: In 1826, Yandaboo Treaty was signed between the British and

the Burmese. As a result, Assam went under the British colonial rule. The British government encouraged large scale of immigration into Assam. The British developed the tea industry in Assam. 

3. Immigration during partition: In 1947, Bengal was partitioned into the Indian state of west Bengal

and the Pakistan province of East Bengal. The majority of East Bengali came and settled in the city

of Kolkata. Later, a number of people moved to the Barak valley of Assam and Tripura.

4. During Bangladesh war, 1971: In 1971, East Pakistan became an independent country and East

Pakistan named was replaced as Bangladesh. During Bangladesh war, around 10.