Where were the Marxist-Leninist (now Maoist) groups or Naxalites particularly strong in India during the 1970s?

West Bengal

There was also an increase in the activities of Marxist groups that did not believe in parliamentary politics. These groups had taken to arms and insurgent techniques for the overthrow of the capitalist order and the established political system. Known as the Marxist-Leninist (now Maoist) groups or Naxalites, they were particularly strong in West Bengal, where the State government took stringent measures to suppress them.