I suppose the Japanese counted on Germany doing its part to deal with the USA.
Here’s a fact many don’t know.
The turning point of the US stock market, the point where the market would go higher and higher after the depression?
The euphoria of the Doolittle raid....
After the Atlantic Conference in 1942, Churchill and Roosevelt agreed to focus the war effort 80/20 on Germany/Japan. The decisiveness of victory at Midway came as surprise to the Americans who managed to seize the initiative with one hand tied behind their back, as it were.
Hitler’s decision to declare war on the U.S., often seen as a huge miscalculation, may have been made in an effort to keep Japan in the game.
BTW, the Doolittle Raid lead to the Battle of Midway. The Japanese wanted to establish forward bases further east to prevent a repeat of the Doolittle embarrassment. In the event, the attempt only accelerated their demise.