The Indian subcontinent from its very inception has been home to an extensively diverse populace, however these people being diverse, were evidently divided along various religious, regional and linguistic lines.
The founding fathers of the nation sought out the below listed measures to help protect the nation from ethnic, religious or regional conflicts and hereby maintain it’s unity.

1) To appease the diverse linguistic masses, no single language was given priority rather a group of 14 language were given the status of official language under the 8th schedule of the Indian constitution. (Currently 22 languages come under the 8th schedule)
2)The founding fathers disregarded concentration of power at a singular level rather a federal structure was adopted to govern the country.
3)To uplift the socio-economic minorities, reservations were instituted.
4)Shared cultural elements such as the national symbol, the national anthem and the tricolour were encouraged and emphasised upon.
5)To do away with regressive social practices, legal reforms were initiated (abolishment of untouchability, law against sati etc)

Hence by using a gradual and flexible approach the monumental task of uniting a vastly diverse populations under a singular national identity was achieved.