Gulab Singh founded the state of Jammu and Kashmir after purchasing the entire territory along with people between the rivers of Ravi and Indus from the East India Company in 1846, for 75 lakh. Hari Singh, the great-grandson of Gulab Singh was the ruler at the time of India-Pak independence. Hari Singh, in the weeks after August 15, 1947, gave no indication of giving up his State’s independence, unlike other 570 princely states in the region. It proved to be the root cause of present day Kashmir conflict. Md Ali Jinnah wanted to meet Hari Singh through the excuse of visiting the beautiful valley to recover his lost health. A state with such a vast muslim population makes clear point to come in Pakistan & Jinnah was over sure about this. His shock found no limit when he knew  that Hari Singh does not want him in Kashmir  even as a tourist. Pakistan then decided to force the issue, and a tribal invasion to drive out the Maharaja was initiated. In the early hours of October 24, 1947 the invasion began, as thousands of tribal Pathans swept into Kashmir. Their destination: the state’s capital, Srinagar, from where Hari Singh ruled. The Maharaja appealed to India for help.

On 25 October, V. P. Menon, a civil servant considered to be close to Patel, flew to Srinagar to get Hari Singh’s nod for Kashmir’s accession to India. By signing the Instrument of Accession, on October 26, 1947, Hari Singh agreed that the State would become a part of India. On 27 October, India’s 1st Sikh battalion flew into Srinagar.  Srinagar was soon secured from the Pakistani invaders but the battles in the larger region were just beginning. When Jinnah learnt of the Indian troops’ landing, he reportedly ordered his acting British commander-in-chief General Sir Douglas Gracey to move two brigades into Kashmir, who refused the request. Pakistan finally did send troops to Kashmir but by then Indian forces had taken control of nearly two thirds of the state. Gilgit and Baltistan territories were secured by Pakistani troops. Meanwhile Hari Singh fleed Srinagar with a convoy of 85 cars and wealth of 500Cr. Loaded in 8 trucks and finally settled in Mumbai. Finally, a United Nations (UN) ceasefire was arranged. After long negotiations, the cease-fire was agreed to by both countries, and came into effect at the end of 1948.

Reference:

http://www.mapsofindia.com/on-this-day/26th-october-1947-maharaja-hari-singh-agrees-to-the-accession-of-jammu-and-kashmir-to-india

http://www.jammu-kashmir.com/documents/harisingh47.html

http://articles.economictimes.indiatimes.com/2013-03-14/news/37713654_1_karan-singh-jammu-and-kashmir-omar-abdullah

https://somensengupta.wordpress.com/2012/03/03/a-nemesis-called-kashmir-a-sin-of-hari-singh-and-we-pay-the-price/