George Kennan, the father of US foreign policy post WWII alludes to the fact why a massive global military presence is needed. He wrote this in a secret memo:
“We have about 50% of the world’s wealth, but only 6.3% of its population…we cannot fail to be the object of envy and resentment. Our real task in the coming period is to devise a pattern of relationships which will permit us to maintain this position of disparity….To do so, we will have to dispense with all sentimentality and daydreamings….We should cease to talk about vague and…unreal objectives such as human rights, the raising of the living standards, and democratization. ...we are going to have to deal in straight power concepts. The less we are then hampered by idealistic slogans, the better.” This admission, ever more relevant as the U.S. becomes increasingly dependent on imports of nonrenewable resources, encapsulates the real purpose of military interventions and the nuclear arsenal; “The exercise of U.S. power is intended to preserve not only the international capitalist system but U.S. hegemony of that system.”
I think it’s pretty self explanatory…