Integration of the princely states into the Indian Union was a major challenge before free India. There were around six hundred princely states in 

pre-independent India, in addition to the territories directly ruled by the British. Britain gave these princely states the option to join either India or Pakistan or to be independent.

The integration was really a herculean task and Sardar Vallabhbhai Patel was the Union Minister entrusted with this mission. He appointed V.P. Menon as secretary of the Department of States, created for the purpose of integrating the princely states. Patel and V.P Menon prepared an Instrument of Accession, which stipulated that the princely states had to transfer their control over defence, external affairs and information and communications to the Government of India.

Following the diplomacy of the government and popular protests, majority of the princely states signed the Instrument of Accession and joined the Indian Union. But some states such as Hyderabad, Kashmir and Junagadti resented. Finally they were also integrated into the Indian union through conciliation talks and military interventions.