Assertion: Some historians, both Indian and Pakistani, suggest that Mohammad Ali Jinnah's theory that the Hindus and Muslims in colonial India constituted two separate nations can be projected back into medieval history.
Reason: They emphasise that the events of 1947 were intimately connected to the long history of Hindu-Muslim conflict throughout medieval and modern times.

Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Some historians, both Indian and Pakistani, suggest that Mohammad Ali Jinnah’s theory that the Hindus and Muslims in colonial India constituted two separate nations can be projected back into medieval history. They emphasise that the events of 1947 were intimately connected to the long history of Hindu-Muslim conflict throughout medieval and modern times. Such an argument does not recognise that the history of conflict between communities has coexisted with a long history of sharing, and of mutual cultural exchange. It also does not take into account the changing circumstances that shape people’s thinking.