India is not a nation, it is a union of nations.
There is more linguistic and cultural difference between Maharashtra and Kerala than between Ireland and Hungary.
Muslims were in Kerala from the 8th century and came peacefully, as opposed to the Muslim presence in the north which came as invasions.
Incidentally, Christianity came to India in 52 AD, with the apostle Thomas, so Christianity in India may predate christianity in Rome
Imagine a world where China 'discovered' Europe and declared it a single country.
That's sorta what The British Empire did to the Indian subcontinent.