/u/Samuel_Gompers has your number. He previously answered:

• Can someone address a brief history of Democrats vs Republicans, specifically the change in Dems from the early 1900s being against civil rights to a more progressive party in the 50/60s leading much social change in the U.S.

• Why was there such a huge shift in the core viewpoints of the Republican Party in the past 100 years?

I hope you find those answers helpful, but an answer related to conditions in the decade specified would be welcome.