The seven states of North East India (now eight with the inclusion of Sikkim) are (clockwise) Assam, Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura and Meghalaya. It is only connected to mainland India by the 22km wide Siliguri Corridor and is elsewhere bordered by Bhutan, Tibet, China, Burma (Myanmar) and Bangladesh. Opened to visitors a couple of years ago, positive moves are now being made to develop tourism.
Only Assam, Meghalaya and Tripura can be visited without PAP (Protected Area Permits) or RAP (Restricted Area Permits). Getting them is possible but not easy for independent travelers though no problem for groups traveling with an Indian Tour Operator who will do all the paperwork. It is advisable you take help of a local tour operator in getting this much needed permits done through in case you plan to travel individually.
Over 250,000 sq km
About 40 million, more then half in Assam.
The people of the region are a mixture of Aryan and Mongoloid origin, most of the tribal groups racial origins being visibly those of the peoples of Tibet, Burma, Thailand and Laos. They consequently have little in common with the rest of India.
Whilst some of the more accessible regions came under British Administration under the Raj, much of the region, being covered in mountains and jungles and home to warring tribal groups such as the notorious 'Naked Naga' headhunters remained off-limits. Although some tribal people fought with the British and Indian forces in the decisive battles in Nagaland that turned back the Japanese in WWII, political unrest continued after Indian Independence, with head hunting raids persisting in remote areas into the 1960s. The situation was further exacerbated by the Chinese incursion into Arunachal Pradesh in1962 when they reached as far as Assam, their gateway to India, before running out of supplies and being pushed back to Chinese Occupied Tibet.
Throughout this time, the seven states continued to suffer from ethnic violence and even today, there are still some freedom movements from both the Bodos of Assam and the Naga people though they no longer seem to receive much popular support. There are also tribal struggles between the Kukis and Nagas of Manipur and similar unrest in Tripura. Additionally, there are some border incursions, particularly from Myanmar and an influx of migrants the area can ill afford, from Bangladesh and Nepal.