They did not support Truman's civil right policies.
The States' Rights Democratic Party, customarily called the Dixiecrats, was a segregationist political party in the United States. It was founded in 1948 as a breakaway wing of the Democratic Party resolved to protect states' rights to enact racial segregation against what they considered to be an oppressive federal government.
The Dixiecrats resisted racial integration and aspired to retain Jim Crow laws and white supremacy against federal intervention.