Another thing the US could have done that Australia couldn't have, at least easily, is import foreign labor as is still being done today. That is, the US could always bring in Hispanic workers from Central and South America along with workers from Caribbean Islands. These could have made up for shortages to some degree.
Australia really didn't have a like source of labor to rely on. I suppose that Indians might have been brough in but that would have been far more difficult to accomplish than the US using labor from neighboring countries.

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