there was active intervention from the central regime - more so through its organs of power, not to prevent inflow of muslims from the East. They knew that more East Pak/BD muslims were allowed to infiltrate in that end, the more would the respective non-Muslim societies of WB and BD be cornered and engaged in local fight for survival. It would only engage, absorb, and neuter the Bengalee radicals - on both sides of the "vishwapremik jive prem kare jei jana" love for Muslims/Islam and the anti-Islamic divide.
The Naxalite movement was penetrated and managed well by the rashtryia agencies, and used to both provoke as well as subvert more mainstream political assertion by Bengalees. In fact the strategy was used also by Sk. Mujib to first use/encourage and then massacre the leftist and even non-Islamism based radicals in BD. So, overall, the Indian rashtra managed to destroy the militancy that could have otherwise been harnessed into mainstream politics and used by the regional forces to perhaps become strong enough to become a headache for dynastic coteries of upper UP. At least two whole generations of political brains were destroyed - as well as brains that could have become useful for more more mundane but more productive activities benefiting whole of India.
Who were allowed to survive? Look at the illustrious figures of current Marxist leadership - for example Brinda Karat, was at Calcutta Uni, in the hotbed of conflict, in the hottest period of conflict. Most of the subsequent CPI(M) topcat leadership - the JB brigade of SFI sourced leadership, survived. Even though others of the same movement were qatl-ed - by a combination of throatcutters and uniformed introducers of iron rods into captive naked women.
That society was crushed, with a view to destroy its political class that survived the Partition gameplan - with all the resources a modern semi-totalitarian state under dynastic leadership and coterie arrangements, could manage, taking inspiration from the Brit model.
I have the deepest possible hatred for the Naxalites, because they helped in the Delhite project to destroy all political forces that would not be dependent on the Delhi group. But they could not have done any teetsy-bitsy harm, if the rashtryia management did not do its bit.
They never risked this on the western borders, because that was much closer to their heartland, the land they identify with. Only exception was when they briefly went out of power as part of the lesson taught to them for having gone out of their brief in helping out Mujib and making a nuke blast. That was the only time when they thought of encouraging the same stuff as they had done in WB, as a time tested means of creating trouble for the split polity at the centre then. Once they got back into power- they moved the entire apparatus/model used in WB to the "west" and cleaned up in a similar manner. The Brit policy of selective military highlighting was also a factor. This is one regime with a mortal distrust of the army, and fear of changing well established ethnic structures in it -too.
Add: there have always been bases of RSS/BJP there. That they have survived at all through the vicious rashtryia campaign is a surprise. If people want to believe that no-Indic bases exist there, I think thats good for the movement.
