I think it matters from the perspective of the regime. The people in US are conditioned to believe in the greatness of US, and their superiority over other cultures. The whole American exceptionalism business basically. As a result, people in the army feel loyalty to the existing power structures and the state. On the other hand, once you start moving to what is effectively a mercenary army sourced from countries the empire has been ravaging, they don't have the same level of commitment to the imperial project.