Most of that 6.4Tn was spent, mostly in USA, but a bit in G20 countries, and probably the odd BN in Iraq and afghanistan, with the locals.
Even if USA didnt go to war anywhere, they probably would have spent most of that.
And I'd imagine per capita spend on water, and electricity grid is still higher in USA than, say er Iran.
I know it sounds like a lot of money, but its honestly pocket-change, spread over 20 years.
When toilet seats cost $5000 and the spanner to fit them is $15,000 thats where the real money is going - not really, but its how USA hides its stealthhypersonic 'youcallwecome' aircraft. One day you may see one. Not sure if that makes you lucky......