The communist West Bengal government explicitly issued a circular twenty years back that all negative references to Islam must be completely removed or toned down to a great extent in all the history textbooks of schools and colleges.
Accordingly, during the 1980s, all textbooks in West Bengal have been edited to remove or reduce the negative things done by Muslim invaders during the 1000 years that they ruled India.
Even some NCERT textbooks too have been rewritten with lies about Hindus in general and Brahmins in particular. These books talk about Brahmanism, according to which throughout the history of India, Brahmins tried to suppress and oppress all other people.
Commies also instructed that Islam must be projected as a peaceful, modern and egalitarian religion and Hinduism as an oppressive and superstitious religion.