Earlier quoted context omitted.
> If the USA declared war when Britain / France did in the late 30s, then France may have not been overrun by the Germans. Uh, no. The US wasn't capable of getting its troops to Europe fast enough in 1939, let alone supplying its troops. The Liberty Ship program only started in 1941. Hitler was already extremely dismissive of the capabilities that the Americans can provide, so any potential future threat the US might…
> Furthermore, how could Japan have turned even a decisive naval advantage into victory against the US? Erm, by conquering the Philippines, China, and Korea. Japan had no reason to invade the US proper, its only goal was conquest of the Asian continent. Japan did conquer the Philippines for a short time, before the US counter-attacked to recapture it. Japan had no reason to conquer the USA. Japan wanted to build the…
You're making the same mistake the Japanese made in 1941. The Japanese assumed that they could kick the US really hard enough, steal a few things, and the US would just go "oh, guess I can't do anything." But in reality, as long as the US had the capability to continue the war against Japan, it would. Even if it had to delay the war with Japan until after Germany was defeated--which was the actual war plans of the US in the 1940s, it just turned out that the US had such insane capacity that it could fight both Japan and Germany--the US still would have brought its inexorable military capacity to bear on Japan.
Wars don't end because the victor has achieved its objectives and want nothing more; they end because the loser has decided not to continue the fight (or, more often, because it finally realizes that it has lost). Britain continued fighting its war against Germany, even when it had no prospects of defeating it (during the Battle of Britain), and it was suffering greatly by continuing the war. Why would the US have decided to quit the Pacific merely from losing its carriers, especially since it would have gained as many carriers as it lost within a few months?
Another point to make: the other two US carriers at Midway were damaged, and the US had four operational carriers in total in the Pacific, even after the Wasp was transferred to bolster the Pacific fleet. Two of these carriers (Wasp and Hornet) would be sunk before the year was out and Essex commissioned. It wasn't until the US started churning out an Essex-class carrier (or two) every month in 1943 that the US had a decisive advantage in the Pacific.
Midway (rather like Gettysburg) is vastly overrated as a crucial turning point in war. It marked the first decisive victory for the winning side, and the start of a seemingly inexorable march to war. But the losing side in both engagements was already dangerously overstretched and would have been unable to actually press its advantage even had it won.