During the partition of the subcontinent on religious lines, it would have been natural for Kashmir, a muslim majority province to go with Pakistan. The blame for that not happening should go to Pakistan according Owen Bennet Jones in his book Pakistan, which I am reading now.
According to Jones, the state of Jammu and Kashmir was established in the first half of the 19th century by a Jammu chieftain called Ghulab Singh. Starting from Jammu he added Ladakh, Baltistan, Kashmir Valley and Gilgit. The muslims lived in poverty and the later Maharajah Hari Singh never cared much about that.
When the subcontinent was to be partitioned, the princely states were faced with the option of joining India, Pakistan or staying Independent. While most states chose to join India or Pakistan, the Maharajah of Kashmir decided to remain Independent. In August, 1947 Jinnah had mentioned that “Kashmir would fall into our lap like a write fruit”.
But Jinnah never did anything to win Hari Singh’s support or as Jones puts it, “Throughout 1947 Jinnah’s approach to Kashmir was inept and at every stage his Indian counterparts outmanoeuvred him”. From 1934, Nehru had established a relation with Sheikh Abdullah and had addressed National Conference rallies in 1945. Once when Sheikh Abdullah was arrested, Nehru came to Kashmir, got himself arrested and met the Sheikh in prison. The Muslim League was totally inept at that time and remained totally passive with respect to Kashmir.
Once the British left, a revolt started in Poonch and spread in the state, which was backed by tribesmen from NWFP who came to support their Muslim brothers. The Poonchi and Pakhtoon tribesmen reached near Srinagar and cut of Srinagar’s power supply. The tribesmen forgetting that they were freedom fighters started plundering and the local population turned against them.
Faced with this threat, the Maharajah had no other go other than to request help from India. But the India would not intervene unless the Maharajah joined the Indian union. So he signed the Instrument of Accession and the airlift of Indian troops began on 27th October. So instead of seeing the fruit falling into his lap, Jinnah saw it fall into India’s lap.