The common feature in the minority communties in India - Muslim, Sikh, Christian, Buddhist, Jain - is that a majority of the population comprises of Dalit and Sudra converts.
The conversions of these segments of society to non-Hindu faiths primarily took place to escape the caste system as all these fatihs believe in the universal equality and brotherhood of man.
The first minority community into which the Dalits converted to was Christianity, as early as the first century AD.
Thomas, one of Jesus twelve disciples brought Christianity to India, landing in the Malabar coast in modern day Kerala.
Historical records show that while Thomas entrusted discipleship functions to five Namboodri Brahmin familes because of their education and literacy levels, members of the Dalit and Sudra communities embraced the faith in larger numbers than the upper caste Hindus of the time.
The substantial growth of the Dalits and Sudra Christian population, however, took place during the colonial periods, with conversion taking place to Catholicism and Protestantism as well.
The second minority community into which the Dalits converted was the Muslim community.
Islam was brought into India first by traders, but it was only when Muslim invaders came to the country that conversion of Dalits and other Sudra communities to Islam took place in large numbers.
Some of them converted to escape the caste system while others converted to escape the taxes levied by Muslim rulers on non-Muslims.
Similarly, conversions to Buddhism, Jainism and Sikhism took place later to escape caste as all these new faiths were a reaction against caste discrimination.
It also remains that a much smaller number of upper-castes who saw the egalitarian vaules fo these faiths too converted to them
Although the conversion has benefited the converts in many ways, they have not altogether escaped it because caste has also infected thess minority faiths because many of the converts brought caste into their new religious communities.
NOTE: You can get very detailed and extensive information about the Dalits in Islam, Christianity, Buddhism, Sikhism and Jainism in the eBook 'The Truth About Dalits'.