A former Union Territory known as the "North East Frontier Agency" (NEFA) until 1972, Arunachal Pradesh (translated as the "Land of the Rising Sun" and reportedly named by Indira Gandhi) sits on the far north-eastern reaches of India, a large chunk of which was drawn out of the Chinese dominion without her consent. The mechanism was the Simla Agreement signed in 1914 between the British Raj and Tibet (which China did not recognize). The Agreement stretched a 'McMahon Line' along the peaks of the Himalayas, corralling into India much of what is Arunachal Pradesh today.
Upon China's seizure of Tibet in 1950, Chinese revanchist urges started to fester until they manifested themselves into an inconclusive Sino-Indo war, which took place between October and November of 1962, coinciding with the Cuban Missile Crisis.
The area is still contested and referred by China and Taiwan as "South Tibet."
It is the largest state among the so-called 'Seven Sisters" of India, which are Arunachal Pradesh, Assam, Meghalaya, Manipur, Mizoram, Nagaland, and Tripura.