Which topic is often used as a theme for studying world history since world war 1

Decolonisation and nationalism

Explanation:

In the modern era after world war I many colonies gained their Independence, this led to lots of pride and nationalism

affirmative action refers to the policies that take gender, race, or ethnicity into account in order to promote equal opportunity.

employers subject to title vii are prohibited from taking race or sex into account in any employment decisions. aa is a penalty for having any job group substantially statistically "underutilized" in any race or either sex. the employer must take steps to eliminate the underutilization, then stop, ending its aa efforts