Can I use a post hoc test if I only have two groups?

Andersonville prison, officially known as camp sumter, was a confederate prison (pow camp) in georgia that was built to house a large number of union prisoners concentrated in and around richmond, virginia. andersonville had no access to supplies. it was chosen because it was far inland and was a safe distance from raids from the north. andersonville prison was the largest confederate prison and was known for its unhealthy conditions and high death rate of union soldiers. what is an ironic conclusion that can be drawn about andersonville prison?