Afghanistan (For both the US and the soviets), Vietnam, Korea. There are plenty of examples of powerful nations failing to break much weaker ones. And to think that any nation could actually take on all the others in a war of conquest is sheer folly.
Korea was largely the US versus China and Vietnam was another weird one. It's like WWI in that people not well versed in the politics of the time and how it escalated tend to scratch their heads and wonder what the point was.
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