Slavery is unconstitutional. There is no exception for war slavery.
If I recall correctly. There was a supreme court case around the time of World War I, In which the Supreme Court ruled that a military draft is not considered a violation of the 13th amendment ban on involuntary servitude.
Of course, the Supreme Court nowadays, if faced with such a case, could overturn such a legal precedent.
“Slavery is unconstitutional. There is no exception for war slavery.”
It’s not slavery. They make you sign a contract. All nice and legal.