1.> The corrupt congress party allowed illegal bangladeshis to be settled in NE (Assam in particular) and added them to the voters list.
2.> A movement against migrants (bangladeshi muslims) settling down in that region gave rise first to protests and later to militant organizations and attack of Bangladeshis.
3.> Once the movement was outlawed in india and branded terrorist organization, they required arms and funding.
4.> ISI quickly jumped in to provide the necessary finance and arms supply with one condition. The movement will no longer be targetted against muslim bangladeshis but other migrants from WB and Bihar in particular.
So that is the situation right now , another gift of the congress communalist vote bank policy.