Context

On January 21, 1972, the three states of Manipur, Tripura and Meghalaya became full-fledged states under the North Eastern Region (Reorganization) Act of 1971.

About

Formation of three States

• While Manipur and Tripura were princely states which were absorbed into India in October 1949, Meghalaya, on the other hand, was part of Assam. 
• The states came into being through the North-Eastern Areas (Reorganisation) Act, 1971, enacted on December 30 that year.
• It resulted in a significant change in the boundaries of India's north-eastern region, dividing it into states and union territories.
• The Reorganisation Act mandated the creation of the states of Manipur and Tripura, which were union territories earlier. 
• It also set in stone the formation of the state of Meghalaya. 
• In addition, the then union territories of Mizoram and Arunachal Pradesh also came into being courtesy of the Act.
• Earlier before the north-eastern region was turned into seven sisters with the statehood of Manipur, Tripura, Meghalaya, Assam, Mizoram, Arunachal Pradesh, and Nagaland, the North Eastern composition consisted of Assam plains from the old Assam Province, the hill districts, and the North Eastern Frontier Tracts (NEFT) of the North-Eastern borderland.

Meghalaya 

• Apart from accounts of the more essential Khasi kingdoms in the chronicles of the neighbouring Ahoms and Kacharis, little is known of Meghalaya prior to the British rule. 
• In 1947, the rulers of the region acceded to the newly independent India. 
• The region was given special protection in the Indian constitution along with other tribal areas, and it retained a great deal of autonomy. 
• In 1970, Meghalaya became an autonomous state within Assam and achieved full statehood on January 21, 1972. 

Manipur 

• Over 500 princely states had negotiated their accession to the Indian union before independence. 
• The rulers of these states signed a document called the 'Instrument of Accession'. 
• On August 11, 1947, Bodhachandra Singh, then Maharaja of Manipur, signed the document.
• The Maharaja signed a Merger Agreement with India in September 1949. 
• Full-fledged statehood was granted to Manipur in 1972, together with Meghalaya and Tripura. 

Tripura 

• Maharajas of the Manikya dynasty ruled the former princely state of Tripura. 
• It was an independent administrative unit under the Maharaja even during British rule in India.
• In the royal chronology of Tripura, around 184 kings ruled over the state before it merged with the Indian Union on October 15, 1949. 
• On January 26, 1950, Tripura was accorded the status of a 'C' category state, and on November 1, 1956, it was recognised as a Union Territory. 
• With its people's sustained efforts and struggle, it gained full statehood on January 21, 1972, as per the North-East Reorganisation Act, 1971. 
• Its democratic set-up further stretched to the village level in 1978 with an election to the local bodies that ultimately culminated in introducing a three-tier Panchayati Raj System.