India and Pakistan’s bone of contention is certainly Kashmir and the issue of who has moral claim over the territory. A historical perspective is needed in attempting to put facts on the table.
History of the disputed land:
kashmir_map
(Map not accurate. Shows the disputed regions and not international boundaries.)
At the time of Independence, India and Pakistan were convincing the princely rulers of several states to join the newly formed union. Most of the rulers in what is India today accepted to join the Indian union. It was the Nawab of Hyderabad and the King of Kashmir, who were undecided. The Nawab wanted to join Pakistan but the Home Minister then, Sardar Patel, played hard with the Nawab and convinced the Nawab forcefully.
The King of Kashmir had not decided which side to join, and mostly preferred Kashmir to be an autonomous region. But Pakistan exerted is control over Kashmir, mostly due to regional proximity and ethnic background, and this triggered India to respond leaving Kashmir and its will in the lurch. There began the problem. Nehru, being the kind of person who plays very straight, sought UN intervention in the dispute. This was much to the disappointment of Patel, who thought of employing the same tactics that yielded results in Hyderabad.
That’s the long and short of this seemingly unending dispute.