Like Alaskaball pointed out extreme background checks on all US soldiers, draft or not, seeing the actively participated in war crimes and crimes against humanity in any and all of the past and present US wars and punishment accordingly should be the way. For the rest radicalization/re-education till they can recognize the error of their involvement and then actively being comrades is a good line to draw

This is better executed the closer to us the conflict is. For lets say Vietnam we cant do any such thing at this point but when talking active boots on the ground we do know that a a big chunk, likely a majority was involved in crimes against humanity and war crimes one way or another. And we do know that the vast vast vast majority doesnt regret em or has reconsidered and is proud , hell a big majority % of em voted for Trump and supported every subsequent war. So in this sense treating Vietnam vets as you would have treated nazi soldiers will have you be correct more than often than not