How have events like the 1921 Tulsa Massacre shaped race issues in the U.S.?

The issue of race relations has existed in the U.S. for a long time. The 1921 Tulsa Massacre was one of the most violent racial attacks in the country's history, leaving somewhere between 30 and 300 people dead, mostly African-Americans. 

How significant have such events been in shaping U.S. society's perceptions of race and racial issues? 

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