India and Pakistan were joined together as part of one big country prior to 1947, under British colonial rule. Before independence it was decided that areas of the old India from which some, but not all, Moslems did not want to be part of India would form a new country called Pakistan - which was to be a purely Islamic state, in contrast to the rest of India which was to remain a multi-religious multi ethnic, democratic state
The new nation called Pakistan was formed in two parts - West Pakistan, bordering Afghanistan, and East Pakistan from the Bengal region of India.
As soon as the newly independent countries, India and Pakistan were formed, the new Pakistani government was dissatisfied with the fact the the beautiful valley of Kashmir had opted to join India under the terms laid down for independence. It was decided that military force could be used to settle the issue and Pakistani armed forces occupied one third of Kashmir before the fighting stopped.
Once the fighting ended, the UN was called in to oversee the withdrawal of the occupying Pakistani forces from Kashmir, so that a vote could be held to ask the people of Kashmir whether they really wanted to join Pakistan. The Pakistani forces did not withdraw and the vote could not be held.