We were in the war by arming England against Germany and China against Japan.
In WWI England blockaded Germany against trade with the US (prior to our involvement), and we did nothing. I live within s few miles of 2 sites that were bombed by saboteurs in WWI (in Lyndhurst & Jersey City, NJ); this was a reaction of German sympathizers here who realized that the weapons made here were killing Germans in a war in which we were officially neutral.
WWII was no different; as a “neutral” we were shipping the weapons to kill Germans to England while officially remaining neutral.
Well, I’m sure we would have gladly sold weapons to the Germans if there had been any way to deliver them (*snicker*). After all, Standard Oil managed to get a few tankers of petrol to Germany through Spain.
But that’s what happens when you surrender control of the sea...