According to the article, what was the cause of the major race riots in the North during the early 20th century?

Answer :

Black workers faced virulent racism on the job as well. In June of 1943 , white workers halted production to protest the promotion of their African American co-workers. Other factories faced habitual slowdowns by bigoted whites who refused to work alongside African Americans.

not really sure if this is the exact answer you were looking for , I don’t know if 1943 is the exact date . but i Hope this helps !