crux of north eastern problems and related christian evangelism etc lies with none other than Jawaharlal Kaul "Nehru" only;
in fact he was one big reason behind islamization of erstwhile Assam (now states separated from Assam in post '47 world) too
read about Dhaka plan of the Muslim League and how they got power in the govt of Assam before independence by coalition with congress; started mass migration of bengali muslims in the Hill areas and in protest many congressi in coalition resigned thus bringing the govt down - that gave a chance to Congress to form a govt there and they did in 1938; but Jawaharlal and his lackies had to intervene that they made their own govt in Assam fall by resignations again in just a year and in some short time it gave a chance to Muslim League again to form a govt after securing enough support
result was land settlement policy that provided each bengali "migrant" muslim with some land in the Hill and Valley areas of Assam for permanent residence
and in big way set an example for bengali muslims to infiltrate in erstwhile Assam-NEFA and successor state; long term result is evident already
coming to christianization of the NE and Nehru's role in it
-> Nehru became Foreign Minister in '47 along with the Prime Minister
-> He had an angrez advisor, Verrier Elwin, a known "missionary" in past; also "Anthropologist and Tribal Activist"
this Elwin subhuman was a known rapist and sexual abuser; particularly he used to sleep around with young tribal girls in name of 'participant observation' ; this Elwin literally advised Nehru against integration and development of these NE states then under single entity NEFA citing reasons of 'preservation of their pristine characters and culture'
; he was appointed as "Anthropological Advisor of NEFA" by Nehru
; and being an Evangelical himself; he gave full free run to those activities in the erstwhile NEFA and related regions while at same time keeping the people and the region almost isolated from mainstream India
-> as if this was not enough; those Evangelicals there used to literally propagate things that 'Govt of India treats you people as foreigners; they literally kept matter of NEFA under Foreign Ministry while leaving rest of the Union (of India) to be managed by Home Ministry' - last line was ironically true because our great Videsh Mantri Nehru used to handle things in the NEFA so this kind of propaganda did work!
-> rest was done by poverty perpetuating socialism that Nehru spread across the country; setting up the situations where they can simply flat out lie that 'ham toh gareeb desh hai ji' and in turn giving free hands to christian evangelics based "missions" there for building schools, hospitals and all BUT also providing free ground for all sort of activities
this kept continuing there for long periods even after Nehru; as Indira had got those tribals acting against evangelical activities in Mizoram bombed with IAF planes and all
end result of all this = A near-total segregation of almost the entire North East for over fifty years. Elwin’s preservation policy left a devastating trail of Churches, inter and intra community hostilities and various secessionist movements for "Christian State of Nagaland" , "Mizo People's Republic" and what not; while rest of the union got to enjoy development and industries and upliftment of people NE got Bibles and Churches and Communism and guns.