The U.S military continues to maintain dominance without having actual boots on the ground. Just having the lion's share of aircraft carriers or assassinating foreign commanders with predator drones ensures the U.S can never be played with.

Americas aircraft carriers are known to be vulnerable to massed anti-ship missiles. This vulnerability increased after the development of the DF-21 missile by China. Their vulnerability became even more pronounced after the development of the 3M22 Zircon missile by Russia. Andrei Martyanov wrote an article about this.

Aircraft carriers are still valuable for projecting power around the world, but their vulnerability to supersonic anti-ship missiles limits their use against peer opponents.

Remember Qasem Soleimani? America took him out with a single missile and Iran couldn't do anything but cry. If they threatened an actual war, the U.S would wipe them off the face of the earth.

And thats the problem in its essence. The U.S. military can fight small wars with airstrikes and special forces, and they can fight nuclear wars, but they really have no capability in between those two extremes. They cannot really fight a conventional war against peer opponents like Russia, China, or even Iran. The U.S. military has degraded in its capabilitys since the Gulf war: The technology is better, but the culture is worse.

America has been around since 1776 and defeated every empire that crossed them. Britain, Spain, Germany, USSR. All destroyed. They're not called "back to back world war champs" for nothing.

In both world wars, Germany had already been heavily battered by the other powers before America entered the fighting. And they never actually fought against the Soviet Union: They merely outlasted them.