Answer :
The United States by far has the most powerful army in the world and there yearly military budget is 650 billion dollars. Though are they the most reliable. Yes in a way that the US army is going to get the job done because of there superior strength and mental training, and Technology. But it depends on you use of the word. Is the United States going to send all military personel to a random country asking for help. Probably not but, if there is major ongoing conflict, or poverty that is affecting millions of people the united states will probably send aid to help. So to sum it up the US army is very reliable when it comes to certain situations.