Final answer:
The 'Solid South' label was applied to the former Confederate States after Reconstruction because they consistently supported the Democratic Party.
Step-by-step explanation:
The label 'Solid South' was applied to the former Confederate States after Reconstruction because they consistently supported the Democratic Party. This unwavering support for the Democratic Party persisted for about a century following the Civil War. The Southern states, referred to as the 'Solid South,' embraced the progressive economic programs of the Democrats during the Great Depression, which helped the poor.