One hypothesis is that the collapse of Euro will hurt the US in the short term as one of the US major trading partners the EU will not be able to buy as many American goods and services and many American banks that lent to European banks will also be hurt.
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After the initial pain of the Euro collapse say 3 years, the US dollar would then be the only game in town, and it’s reserve status would be cemented for at least another 10 years.