Why is race considered a "social construct"?

The red race is the race of social construct.

Explanation:

W. E. B. Du Bois considered race as social and cultural differences within different populations of people.

The opposite of peoples belive that race is more of biological and physiological.

He said that the black and white did not care about the the scope of human diversiry hence making the red race as one that did not use race as a measure of distinction.