I don't have a citation or link handy at the moment, and I don't have the ability to find one right now, and I'm going by memory so I will preface this by sayin

I don't have a citation or link handy at the moment, and I don't have the ability to find one right now, and I'm going by memory so I will preface this by saying it's entirely possible that I am wrong here, but I believe in the case of the US the military, both the officer and enlisted ranks, have been increasingly coming from fewer families and increasingly wealthier families. This isn't to say they have been coming from the top income brackets, although this may be true for the officer ranks, but instead solidly middle class backgrounds.