a) The American Empire is more or less finished due to overconsumption
b) Military spending is not the root cause. Expressed in percent of GDP/capita it is at its lowest level since end of WW 2.
Why the overconsumption, the deficits? Simple: Triffin’s paradox. You can’t be the word reserve currency without exporting said currency; i.e. running a trade deficit, thereby hollowing out your own industries.