The Army is fundamentally a real estate focused organization - their role is to take and hold territory.
The Navy is about slow influence - control of the seas allows you can deploy and retract the threat of physical violence depending on the political situation.
The Air Force is about the ability to deliver devastating violence on space-age timelines. But they still require targets.
My cautiously optimistic view is that these forms of violence become far less relevant when geography is no longer the key dividing line in tribal affiliation. You will see a rise in low level violence, and that will be associated with a decline in the primacy of the nation state. But it will reduce the risk of globally devastating conflict.