These aren't born warriors. They are built. The all seem to have joined up young and spend many of their formative years in the military. They are not born/bred into military units, nor were they raised from birth as fighters.

The fact that young men take to soldiering isn't unusual. There is some feedback here. Soldiers create the environment that creates people like themselves. Visit any US-allied base to see what I mean. The US is a very young force, with kids joining up and leaving before hitting 30. That makes the US today very similar to the US during the Vietnam era or the UK during WWI/II. This results in a very different culture than in other nations (Canada, Germany, AU) where soldiering is more of a career. Young men create around themselves an environment that supports them. It is therefore no shock that they feel more at home in that rarified environment.