"Under the North Eastern Region (reorganisation) Act, 1971, Tripura, Manipur and Meghalaya became full-fledged states Jan 21, 1972," Tripura Chief Secretary Sanjoy Kumar Panda said at a function in Agartala.
"Tripura and other northeastern states achieved many successes but to develop these states at par with the mainland states, much remains to be done, be it in terms of economic development or rooting out terrorism," he added.
"With militancy on the wane, Tripura is witnessing rapid development in sectors like natural gas, forestry, rubber besides progress in horticulture, agriculture, health and education," Panda said while addressing the main function on the occasion at the Town Hall.
The erstwhile princely states of Tripura and Manipur merged with India Oct 15, 1949, and became union territories before getting the status of full-fledged states.
Meghalaya was formed as an autonomous state April 2, 1970, after being carved out of Assam.
Manipur Governor Gurbachan Jagat said in a message in Imphal: "Manipur is still lagging behind in many spheres of development and hence there is need to hasten up the progress of development and growth."
"The benefits of development should be made available to all citizens irrespective of community, caste, creed, language and religion," Jagat said.
The governor also expressed hope that Manipur with its rich human potential would rise above all parochial interests and work to become a more prosperous state.