Assam was affected by influx of migrants from East Bengal since the 1920’s. As time passed, the illegal immigrants encroached on the lands set apart for professional grazing reserves. The concern for rapidly increasing number of refugees arriving from East Bengal and later newly formed East Pakistan in the 1940s, created tension among the Indigenous Assamese people and many tribes in the state.
The first influx of refugees in considerable number was in October 1946 following the Noakhali riots. Between 1948 and 1971, there were large scale migrations of all religions from Bangladesh (then East Pakistan) to Assam. By May 1949 the number of total immigrants not limited to only Hindu or Muslims reached two-and-half lakhs. In 1971, after the Pakistani crackdown in East Bengal, more than one million refugees sought shelter in Assam. Many of them went back after the creation of Bangladesh, but a vast majority remained. After 1971, there occurred a fresh, continuous and large-scale influx of land-hungry Bangladeshi peasants into Assam
However land in Assam had by now become scarce. The 234,568 sq km undivided Assam became 78,438 sq km after all the different states were carved out. The indigenous Assamese people feared loss of their holdings and the demographic transformation generated widespread feeling of linguistic, cultural and political insecurity, which overwhelmed the Assamese and imparted a strong emotional content to their movement against illegal migrants in the eighties. The demographic transformation of Assam created apprehension among the Assamese that the swamping of Assam by foreigners would lead to the Assamese being reduced to a minority in their own land and consequently to the subordination of their language and culture, loss of control over their economy and politics, and, in the end, the loss of their very identity and individuality as a people. Though illegal migration had surfaced as a political matter several times since 1950, it emerged as a major issue in 1979 when it became clear that a large number of illegal immigrants from Bangladesh had become voters in the state. Even though there is no definite figure of illegal immigrants, the National Register of Citizens puts the number at 1.9 million while unofficial figure could be as high as 20 million. In a state where 13 million people speaks the Assamese language, this demographic change will make Assamese a minority in their own state.