Segregation means to separate groups of people based on race or cultural differances. Segregation can be forced or self-imposed.
In the southern United States, the policy was created by state governments at the end of Reconstruction in 1876 and the reemergence of Democratic party control of Southern state legislatures. The Democratic party has been known as the party of segregation ever since.
Woodrow Wilson, the second Democrat president after the Civil War, introduced segregation into the United States government Civil Service, requiring separate bathrooms and cafeterias in federal buildings and installations throughout the land, including Northern and Western states which had fought for the Union and existed without laws requiring segregation of the races. US military training and units also were segregated.
Segregation was allowed in public schools by the U.S. Supreme Court in Plessy v. Ferguson (1896), but then reversed after 20 years of Democrat control of both Houses of Congress and the presidency when President Eisenhower appointed former California Republican Gov. Earl Warren as Chief Jusiice. The Warren Court ordered school desegregationin in Brown v. Board of Education (1954). As a reaction in the 1960s, Democrats "wanted policies that privileged whites."
In addition to the public schools, segregation existed in the United States military up until 1947. In the Democratic controlled South and federal government it existed in public accommodations like restrooms, drinking fountains, cafeterias, movie theaters, buses, trains and hotels before the federal government reversed itself and banned it with the Civil Rights Act of 1964.