The riots didn't start all of a sudden in 1947... There were riots, huge ones, all across the country in the 50 years preceding them as well... Traditionally, as a thumb rule, hindus and muslims haven't been too friendly to each other... Moreover, Muslims were scared (whether rightfully or not) that they will be swamped by the Hindu majority in an independent India... Over that Mahatma Gandhi's unwanted tilt towards Nehru resulted in alienation of Jinnah... and the man who had always opposed the partition of India, ended up becoming Pakistan's father of the nation....