Until 1954, state-supported and sanctioned segregation along racial lines was completely legal, and school administrators often refused to allow black, Hispanic, or Asian American children to enter a school building. What is this an example of what?

It is an example of racial segregation

Explanation:

Racial segregation can be defined as a practice whereby one or more races make themselves superior by restricting other races to certain economic or political advantages, situations, areas of residence, institutions (like games, schools, and churches) and facilities (toilets, social amenities, restaurants, etc.) - because they feel superior to the other races.