They never claimed Americans are the only ambitious people, or even the most ambitious. Just “very ambitious”, in a list of factors that (put together) allegedly combined to explain the notable outcome.
There are other countries that can’t be invaded, or speak a single language, or have a large market, or have ambitious people, or culturally permit failure without ostracizing people.
There are other countries that can’t be invaded, or speak a single language, or have a large market, or have ambitious people, or culturally permit failure without ostracizing people.