1948
THE DIXIECRATS:
Southern Secession from the Democratic Party
In 1932, Franklin D. Roosevelt became the first Democrat to win the White House since Woodrow Wilson. In his first 100 days, Roosevelt launched an ambitious slate of federal relief programs known as the New Deal, beginning an era of Democratic dominance that would last, with few exceptions, for nearly 60 years.
Roosevelt’s reforms raised hackles across the South, which generally didn’t favor the expansion of labor unions or federal power, and many Southern Democrats gradually joined Republicans in opposing further government expansion.
Then in 1948, when President Harry Truman (himself a Southern Democrat) introduced a pro-civil rights platform, a group of Southerners walked out of the party’s national convention. These so-called Dixiecrats ran their own candidate for president on a segregationist States’ Rights ticket that year; their candidate, South Carolina governor Strom Thurmond, got more than 1 million votes.
Most Dixiecrats returned to the Democratic fold, but the incident marked the beginning of a seismic shift in the party’s demographics. At the same time, many Black voters who had remained loyal to the Republican Party since the Civil War began voting Democratic during the Depression; that trend continued in the following years, and Black voters voted Democratic in even greater numbers with the dawn of the civil rights movement.
Source
History.com – How the Party of Lincoln Won Over the Once Democratic South