What are three reasons the Kashmir issue was a problem for Pakistan in 1947?
The Kashmir issue was a problem for Pakistan in 1947 for three reasons:
1) When the British left India in 1947, there were about 600 princely states up for grabs among Muslim and Hindu factions. Kashmir had always been a Muslim majority state, and Pakistan was anxious at the possibility of it acceding to India. Had Kashmir been part of British India, it would have definitely joined Pakistan, since Muslims constituted more than two-thirds of Kashmir's population. Since Kashmir was sovereign, however, India felt that it had equal claim over it. India went so far as to bring its claims to the attention of the United Nations after Maharaja Hari Singh (Kashmir's Hindu ruler) ceded Kashmir to India in October 1947. So, Pakistan went from being sure of Kashmir to battling Indian forces for it. This put Pakistan in a weaker position, both politically and militarily.
2) Many citizens in Kashmir favored complete sovereignty or even accession to India. So, this was a problem for Pakistan in the public relations arena as well as the military one. Many Kashmiri Muslims appreciated India's open attitudes towards pluralism and secularism, attitudes that proved problematic for Pakistan. In 1947, Pakistan came to realize that it would have to engage India militarily and reluctant Kashmiri Muslims ideologically.
3) India's claim to Kashmir also had a legal foundation. In 1947, the Hindu ruler of Kashmir, Maharaja Hari Singh, signed the Instrument of Accession, legally ceding Kashmir to India. So, India's legal argument was to prove problematic for Pakistan in its mission to claim Kashmir for its own.
Kashmir is a region with a very long history, and ties to both Hinduism, Islam, Sikhism and Buddhism. Today most of the population is Muslim, but there are many important historical sites there that are highly valued by Sikhs, Hindus and Buddhists as well.
So that is what I'd put as the number 1 reason: The conflict over Kashmir is a conflict over a region with significance to multiple different religions.
The second reason is the partition between India and Pakistan in 1947, where what was once a single colony under Britain became split into two countries, approximately--but not precisely--making India a country of Hindus and Pakistan a country of Muslims. Kashmir was right on the border, and both India and Pakistan wanted it; so the compromise was made splitting it in half (akin to East and West Berlin around the same time). In fact Kashmir is mostly Muslim, so Pakistan probably had the better claim; but India is economically and militarily stronger.
The third reason is that Kashmir itself had a quasi-independent government in 1947, and was trying to become a third independent country separate from both India and Pakistan--something that neither India nor Pakistan was willing to allow.
India and Pakistan been fighting over Kashmir on and off ever since, and now they have nuclear weapons pointed at each other.