Because of ye grande Islamic Nationalism, and a man named Muhammad Ali Jinnah. http://en.wikipedia.org/wiki/Mohammad_Ali_Jinnah

Religious differances between people of Islamic faith and Hindu's. Muslims immigrated to what was once part of India and became Pakistan while all the hindus in this region left and migrated back to present day India.

Its concomitant partition into the separate countries of India and Pakistan resulted in a tumultuous migration of Muslims to Pakistan and Hindus and Sikhs to India in which approximately one million people died. Kashmir is still a severe bone of contention and cause of much trouble between the two countries. The split was when the Country, India, gained its Independence from the UK in 1947. Hostilities between India and Pakistan broke out again in 1971 this was when many people died. The answer is Religious differences, as seem to be the case in most wars and divides.

The British knew they had to get out of India, and wanted to do it fast. They thought (assisted by advocates such as Jinnah) that if they left a united India, the Muslims (who would be in a minority in the united country) would not be properly treated by the Hindu majority, so they decided to create two countries in which each would be the majority faith. What would have happened if they had not done so is an unanswerable questions. A similar division didn't work very well in Ireland, but other countries such as Czechoslovakia have separated peacefully.

Well, I think it was NOT only religious differences. There were several people in the then India who wanted a separate country for themselves - and were extremist. No matter how much politicians and British wanted to create Pakistan, it cannot happen if the people don;t want it. So basically, all the muslims who were either scared of living in a majority hindu land, and those who were extremist in a way that they don't want to tolerate people of other faiths, moved to 'Pakistan' to create an islamic country. The rest of the muslims, and most of the hindus, christians, sikhs in the 'Pakistan' territory who did not want a religious rule came to India - a secular country. India is not a hindu country, per say. We have Manmohan Singh as our PM (sikh), Abdul Kalam as our ex president (Muslim), Rajiv Gandhi (parsi), in our history of PMs and presidents.... and all the indian muslims in india (most), strictly identify themselves as Indian, and are very much at peace with the rest of us. This is the foundation of any major democracy- even US, canada. Pakistan on the other hand - has its extremist elements growing, and off late have shia-sunni (intra muslim) riots too... It's obvious that any country which was formed because they cannot live with another's culture, by nature has an extremist core, and will keep finding differences among themselves. The british, and the then muslim league just voiced the opinion and helped these people get what they wanted then... the real reason was the people who wanted a separate country!