I believe modern militaries have one traditional purpose (to resist foreign invaders) that is largely outmoded among so-called superpowers, and three more relevant modern purposes:

1. to frighten the vast populations of the modern superpower/nation state into submission and apathy by virtue of the vast killing power of the superpower’s weaponry
2. to intimidate lower-GDP nation states with less weaponry into doing the will of the regional or global superpower; and
3. to, via occasionally hot or persistently warm ‘brush wars’ conducted in underdeveloped proxy nations, efficiently destroy excess military-industrial complex hardware and/or gain access to resources (oil) in order to stimulate new production and economic growth among favored constituents and industries.

The rest is hogwash.