The third alternative is correct (C).
The context of the Battle of Chickamauga was post-independence and with a divided country with half of slavers and half of libertarians.
In this context, the Battle of Chickamauga, which took place between September 19 and 20, 1863, involved approximately 60,000 soldiers fighting for the Union and faced 65,000 Confederate soldiers and represented an important step towards the Union's victory in that region of the South.
After a great conflict with great losses the Union had to withdraw, allowing the victory of the Confederation. But in November of that year, the Confederation failed to maintain its dominance over the region, losing it to Union troops, which represented an important step towards the Union's victory in the southern United States.