Does the trauma of war buside the more you are exposed to it ?

Many American soldiers return from one or 2 tour of duties traumatized. However (surviving) Wehrmacht soldiers killed 100s of soldiers over several years, if they were in the right ss units they offed whole cities (civilians) some ended up even pows for 10+ years and although they prolly dreamed some of it up at night they lived on pretty normal lives. Does the initial suffered traum subside if somone is exposed to more of it and it becomes "normal" ?