Hyderābād State was an Indian princely state located in the south-central region of India, and was ruled, from 1724 until 1948, by a hereditary Nizam. The capital city was Hyderabad.
At the time of the partition of India, the State of Hyderabad was the largest of all princely states in India. It covered 82,698 square miles (214,190 km2) of fairly homogenous territory and comprised a population of roughly 16.34 million people (as per the 1941 census) of which a majority (85%) was Hindu. Hyderabad State had its own army, airline, telecommunication system, railway network, postal system, currency and radio broadcasting service.
Nizam decided to keep Hyderabad independent. The leaders of the new Union of India however, were wary of having an independent - and possibly hostile - state in the heart of their new country. Most of the other 565 princely states had already acceded to India or to Pakistan voluntarily. The Indian government was therefore determined to annex Hyderabad into the Indian Union, by force if necessary.
In September 1948, India launched a military operation named Operation Polo, led by Sardar Vallabhbhai Patel, then Minister of Home Affairs and Deputy Prime Minister of India. The Indian Armed Forces invaded the State of Hyderabad and overthrew Nizam.