What about historical events that are racist or sexist, is it okay to talk about them in my class?

Yes. Discussion about historical events, even events that are difficult to talk about, are important to include as appropriate to the subject(s) of your classes. However, you may not tell students in your class that they are responsible for those events, or that they should feel guilty simply because they are of the same race, color, national origin, or sex of those who were responsible for the events.