In the context of the question, the state that held lengthy debates about whether to secede from the Union but eventually decided to join the Confederacy was South Carolina.
1. South Carolina was the first state to secede from the Union on December 20, 1860, following the election of President Abraham Lincoln.
2. Before seceding, South Carolina engaged in heated debates and discussions regarding its position within the Union.
3. The state ultimately chose to join the Confederacy, becoming a key player in the secession movement that led to the American Civil War.
Therefore, the correct answer to the question is:
D. South Carolina
