No army on earth can defeat the russians in a ground war. It is impossible.
No country can defeat a stockpile of nuclear weapons. Ergo, Russia, USA, and China cannot be ‘defeated’ without suicidal consequences. Although Russians and Chinese have long records of killing off their own people – which is what concerns westerners.
That said, there is no power on earth today, nor none in history that can survive a war with the united states – given any time. The only way to attack a country like the USA is with a surprise and deeply. Even so, that would mean suicide.
https://www.quora.com/Is-there-any-army-in-the-history-of-mankind-past-or-present-that-could-possibly-defeat-the-United-States-as-it-stands-today-What-about-as-it-was-in-1950