The USA joined WWI to a large extent due to money - American commerce would maximize profits, and willingly, by insuring that the Entente fought the war to victory. But the bankers had a far greater vested interest. They were lending money, which would be repaid only if Britain won. Therefore, as the amount of money actually borrowed by Britain increased, the American bankers became more committed to insuring, specifically, an Entent victory, a crushing Entente victory.
The USA wanted France to pay back its loans so that was a primary reason America joined the war in March 2018 (when troops came to Europe).
The USA joined WWII because the Nutzis and Japanese were a real threat to the USA. And that involved saving France incidentally.
We didn’t join either war “to save France”
Japan and Germany both declared war on the US in December 1941 before the US declared war on them.