Prisoners of war aren’t supposed to be punished. The basic idea is that they’re detained to prevent them from returning to the fight. The Geneva Conventions all

Prisoners of war aren’t supposed to be punished. The basic idea is that they’re detained to prevent them from returning to the fight. The Geneva Conventions allow them to send letters, buy things, receive pay, recognize their own hierarchy, etc. The Geneva Conventions also allow them to be detained without charge until the end of the war. If they have committed certain crimes, then they can be convicted and held after the end of the war, but that’s something of a special case. Many Confederate soldiers during the Civil War never understood this (remember, the Union declared that the South couldn’t secede, which would have made all Confederate POWs US citizens).