Perhaps it’s not quite accurate to claim that “World War II wouldn’t have happened” if Germany hadn’t declared war on the USA four days after Pearl Harbor. There’s this tiny little place called Europe and in 1939 Hitler invaded Poland, which made the supine appeasement-oriented British finally understand that giving a shouty little man everything he wanted wasn’t actually going to be the stable genius plan they’d thought it was. And so from 1939 onward there was this thing called World War II that included not only that tiny place Europe that no one (in the USA) has heard of but also very obscure places like China and Korea and Malaysia and North Africa that presumably no one in the USA has heard of either.
All these hard-to-remember countries would probably argue that all the invading and killing and destruction was actually World War II even if the USA wasn’t involved until much, much later.
Here’s a thought: maybe someone should write a history book for US children explaining all of this?