The Indo-Pakistani War of 1947 and 1948 resulted in the creation of what is essentially the current border between India and Pakistan. The war began when Pakistan invaded Kashmir. On October 22, Pakistan sent troops to capture the region in response to a Muslim uprising against Hindu landowners. The Pakistani attack caused a flood of Hindu refugees flowing into India. This even further heightened the intensity of the civil war that was currently being fought in India.
From a geopolitical view, the Pakistani attack prompted the Kashmiri ruler to join the Indian nation. It was immediately clear that this was merely a ploy to procure military assistance, which Kashmir requested from India upon its joining of the nation. India agreed to give aid and sent Sikh troops into Kashmir, meaning to push the Pakistani troops out of the region.
Mohandas Gandhi’s assassination (January 30th, 1948) put a periodic end to the fighting between India and Pakistan. When fighting broke out again in April of the same year, the U.N. intervened to establish a cease-fire. The battle lines as of April 1948 became the essential border between the two nations. Tensions over this armistice are still prominent today.