Big three educational textbook publishers

McGraw Hill is the biggest, providing education textbooks for Kindergarten through post grad studies.. it is the most widely used of the publishers.

https://www.mheducation.com

https://en.wikipedia.org/wiki/McGraw-Hill_Education

The other two are Pearson

https://www.pearson.com/us/

https://en.wikipedia.org/wiki/Pearson_Education

and Mifflin Harcourt

https://www.hmhco.com

https://en.wikipedia.org/wiki/Houghton_Mifflin_Harcourt

Putting these up since Q dropped the crumb about looking at textbooks.

IF ANYONE HAD A HAND IN CHANGING AND SUBVERTING HISTORY IN TEXTBOOKS, IT IS THEM.