There's two issues. The one is that prosperity is already very ambiguous, and in the context of nations we usually default to easily measurable things like GDP. This doesn't define human well-being which is actually not so easy to measure. Look at the US as the richest nation on earth for a stark example. The question was asked in this way and without this clarification for a reason.

But the bigger issue is that it's just the wrong question to ask. Any definition of prosperity for one massive people can be built upon the cruel subjugation and exploitation of others. And that's exactly what happened and continues to happen under the "former" global colonial powers, as well as aligned governments (which includes a lot of puppets). Hence US foreign policy. Celebrating this as a victory of capitalism is either clueless or outright malicious.