How many slave states joined the Confederation during the American Civil War?

In total, 11 states fought on the side of the Confederation. At the same time, 20 non-slave states and 4 border slave states fought on the side of the United States. The governors of Kentucky and Missouri were in favor of leaving the United States and joining the Confederation. True, part of the population was in favor, and part was against. As a result, these states became neutral, but nevertheless, volunteers from these states simultaneously replenished one and the other army. In general, the numerical superiority was behind the North, which made it possible for him to win.