Briefly explain the reasons for the civil disorder that occured after the independence of Kashmir.
First of all, please note that Kashmir is not a country and so has never gained independence. In this answer, I will address unrest that occurred in Kashmir when India and Pakistan gained their independence from Great Britain.
In 1947, the United Kingdom granted independence to its Indian colony. In the process of becoming independent, the colony split between majority-Muslim Pakistan and majority-Hindu India. Kashmir was largely Muslim but was ruled by Hindus who ceded the area to India. This caused a great deal of unrest as the Muslim inhabitants of the area (aided by Pakistan) protested being made a part of India. This led to clashes between Muslim inhabitants and the troops that India sent to the region.