The changes removed or shrank references to Hindu extremism, the country’s secular foundation and India’s long Muslim history.

When Indian children began the school year this week, students in thousands of classrooms were issued new textbooks on history and politics that either watered down or purged key details from India’s past that Prime Minister Narendra Modi’s ruling party finds inconvenient to its Hindu nationalist vision for the country.

The changes took aim at references to the links between Hindu extremism and the assassination of Mohandas K. Gandhi; the secular foundation of post-colonial India; and the 2002 riots in Gujarat, where hundreds of Muslims were killed in days of indiscriminate retaliatory violence at a time when Mr. Modi was the state’s top leader. Chapters on Mughal history, covering hundreds of years of Muslim rule, were either slashed or removed.

Among the deleted passages from 12th-grade history and politics texts: