The soldier oath, or Oath of Enlistment, is a pledge taken by U.S. military recruits to support and defend the U.S. Constitution, bear true faith and allegiance to it.
I think that is the bottom line here.
That has nothing to do with making them a Western man, if America in 1790 had the immigration we have today and all of them pulled a hitch in the military we would never have become ‘America’, just as immigration since 1965 has largely erased America and will erase us completely eventually.