How did the princely state of Manipur accuse to India?

Due to integration of princely states, Maharaja of Manipur Bodhachandra Singh signed the Instrument of Accession with the India Government on the assurance to be maintained the internal autonomy of Manipur:

1. The state became a constitutional Monarchy after it conducted elections in 1948 to become first state to hold elections based on ‘Universal Adult Franchise’. 

2. But sharp differences arose in Legislative Assembly over the question of merger of Manipur with India while the state congress wanted the merger other political parties were opposed to this.