Likely none. China has the man power but not the resources. Russia is a full tech level in aircraft behind USA. The U.S. Navy under Obama was bigger than the next five biggest Navies combined. The Abrams is still one of the most advanced and effective tanks to date with 120mm cannon (biggest guns in WW2 were German tiger 2 at 100mm) and anti tank missiles, depleted uranium rounds. The United States army is one of the best trained in the world. For instance; in ww1 the dough boys showed up and in less than a year it was over. When fully militarized, USA can produce all except maybe China. If you play by Geneva rules, no country or coalition could be powerful enough to defeat USA. For instance the Bush family owns like 3 or 4 of the handful of super tankers in oil. Their first goal would be to secure crude oil to use their tech because oil is single handedly the biggest weakness in their logistics and arguably their biggest military weakness. Over night, they can raise almost a 20 million man army due to selective service. They could potentially raise an army of a hundred million service members if raising the draft age from 18–25 to 18–35 and if you include women you effectively double when including woman. So with current plans we can build an army bigger than many countries total population. Not to mention drone strikes which are basically flying armories. Equipped with state of the art cameras which have night vision and other filters such as thermal vision. They have guided bombs and missiles strong enough to destroy tanks and fly for 14 hours up to 300mph. All flown from a base somewhere in Texas or an air Force Base deep in the states.

Long story short nothing short of M.A.D (mutually assured destruction) would stop them. While typically associated with nuclear weapons they may also include bio weapons such as engineered plagues. The enemy couldn't make any vaccines because the enemy would find it eventually. Megadeaths would occur in war with United States (term created for nuclear bombs a quantity that is 1 million deaths). Human wave and trench fighting would likely occur as offense and defense call for mass invasion and retreats each side would dig in and find village to village. It would be across between WW1, WW2, Korea and Vietnam with mortality rates higher than the Spanish flu. The world would be utterly destroyed in Vietnam the US dropped bombs by the tons. Entire Creed's, families, ethnicities, religions, social structures, monuments and natural landmarks would be obliterated in under a year. That's what would happen.