"Having the largest army or most powerful doesn't mean you can take out EVERY other country, unless you plan on nuking them... In that case, there's nothing left for you to take... Which leads me back to the "dying slowly" So yeah, there goes that."
You make it sound like all the US can do is nuke. Having a powerful military involves much more than nuclear warfare. If the US decided to take over Canada, nukes wouldn't need to be used...same for Mexico. Your land would still be usable...preventing the "slowly dying". Sure, nukes can be used on Russia, China, or some other huge threats...but it's not like the entire world needs to be nuked.