There are many aspects of this relationship you have missed, including some quite dark ones.
Perhaps the most important is America's reluctance to go to war against Germany.
It was, in the end, Hitler who declared war on America.
Not only was America reluctant to go to war against Germany, but forms of fascism were very common in America during that period.
The American Bund, looking for all the world like Brownshirts, was a huge organization and held a gigantic rally in New York City.
Many wealthy Americans had close business relationships with the Nazis. Texaco traded fuel right up into war. IBM assisted in record keeping systems. Disney used to send special copies of his new cartoons to Mussolini, who was a great fan.
Henry Ford's photo hung over Hitler's desk at his chancellery. Hitler admired Ford's ideas on race and race improvement, which were quite revolting.
Indeed, before Hitler hit his full stride, the biggest program of eugenics in the world was in America. Tens of thousands - typically people with low IQs but sometimes other "undesirable" types - were ordered involuntarily sterilized under the oppressive laws in America.
Few Americans know it, but the way the Pledge of Allegiance (itself a questionable thing in a supposedly free society) was given, right up until about 1940, was by stepping one foot forward and extending the right arm up, just like the Nazi salute.
By the way, your reference to America’s victory over Germany is quite inaccurate, though commonly believed in America.
It was Russia, at the cost of 27 million lives, that rolled over the Nazis. They fought the greatest single battle in all of human history, Stalingrad. They fought the greatest tank battle ever seen, Kursk. And they endured horrors like the siege of Leningrad where the dead were piled like cord wood.
America bombed and bombed – killing hundreds of thousands of innocent civilians - but according to no less an authority than Albert Speer, Germany kept its armaments production going well to the last days. And, as we all know, even the death camps went unscathed.
When it looked like the Russians would roll right over Europe, America joined the battle in a serious way, but Germany was effectively already defeated. America’s great Battle of the Bulge from that period, was rather a squib of a battle compared to something as titanic as Stalingrad.
America’s total losses in WWII were roughly one-half of one percent of the more than 50 million souls who perished.
