Upon reading your first post, it seems the US was beholden to foreign interests i.e. foreign creditors.
These foreign creditors would have demanded payment in gold and silver. Gold and silver coin that there wasn't much volume in the US at that time in addition to the gold/silver ratio constantly draining the monetary supply having a deflationary effect on the monetary supply and the economy.

Interesting fact: the Continental and the Greenback were fiat currencies that were just as instrumental in the United States winning its skirmishes just as much as armaments.