Why did so many race riots / race massacres occur during and immediately after WWI?

Why is it useful for historians to base certain studies on the analysis of historical themes

What did the u.s. want to build on the land acquired through the gadsden purchase?

In which supreme court case did the court rely on the concept of implied powers to make its ruling? a) gibson v. ogden b) mcculloch v. maryland c) dartmouth college v. woodward d marbury v. madison