Since someone posted a list of France's military history, lets take a looksee at all the conflicts America has had over the years. Has America ever won anything against a competant military power without assistance from another country?
Well of course, someone had to hold our coats...
It's easy to poke fun, but the reality is that almost every major war of the past 300 years has involved alliances. Some were more trouble than others. Some were nearly useless (visualize Germany having to intervene in Greece, when the Italians were defeated or a small Brit force driving those same Italians out of North Africa). Others bore the brunt while Allied nations mobilized both their military and industrial bases (the USSR). Even so, modern scholarship shows that it was highly unlikely that the Soviets would have survived 1943 without the vast Lend Lease program.
The United States fought only one major war by itself, our Civil War. When it ended, the USA had the most powerful military on earth, and a huge fleet of ironclad warships. What did it do with that vast military power? Nothing. Nothing in terms of international events. The USA turned towards itself, and expanded on the continent, disbanding much of that military power. It was the nature of the culture.