To answer the question, US has the strongest military in the world. However, being the strongest doesn't mean you can win every war or would it make sense to. As it stands and the way wars are fought now, it might only be beneficial to fight a country with significantly less meanwhile also getting funds and assistance from allies. IE: Afghan and Iraq (look how high the cost is even for those wars). So strongest military doesnt mean you can attack a country with a strong enough military deterrent Ie: Russia, China and etc.
The title of being the strongest just doesn't carry as far as it use to anymore with globalization and how major countries all need to depend on each other one way or another, combined with weapons of mass destruction available from both sides. Russia isn't afraid of the US just because they have a stronger military, cause they know the US wouldn't risk a fight.