What if WWII was fought in American soil as well?

If you are imply that the Japanese or nazis took the fight to the american homeland.

That wouldn't end well.

American is a vast country, connecting shore to shore, so much logistics would be needed to support an army. Which neither germany nor japan could do.

It would be literally impossible for either to have the logistics to do that. (if the war lasted more than 6 years, war wages on for decades, with new technology that could change.)

Neither could beat america's industrial might. They wouldn't be able to outcomplete the americans in the manufacturing of weapons,planes, and tanks without having to take a vast amount of land.

America would probably suffer greater losses than it did, but it would most likely be no where as near as bad as europe.

America did take advantage of being one of the allies with the least bruises after the war, while europe had to rebuild.

tl;dr

Logically america wouldn't be set back so far.

Very impossible...if you're talking about the mainland off course (the Battle of Aleutian islands is the only battle fought on American soil during the Second World War since Alaska was an incorporated territory unlike the Philippines).

The Axis powers didn't have much of a capability to connect logistics to logistics across thousands of miles of water to the U.S., especially that the Axis were fighting enemies that were extremely close to their shores.

To do this, they would have to get through their enemies very close to them first before thinking about going thousands of miles across the ocean to the continental U.S. None of them possessed anything to mount that kind of thing, hence, making their invasion of the continental U.S. as a plan extremely moot.

Even if they did have a strong navy, our B-29s, our submarines our munitions, our well-trained soldiers, as well as the American civilians armed with guns would have no doubt inflict as much damage to the enemy's air, naval, and ground forces to the point they would be screaming their asses back to where they belong. Our country is very vast and it was too much for the Axis to handle far worse than when they invaded the Soviet Union.

Simple, is that the Axis powers neither possessed any capability to invade the continental U.S., it's just suicidal and dangerous to risk that kind of operation.

(1) Technically, the Aleutians and some of the other Pacific Islands invaded by the Japanese WERE American soil.

(2) WWII couldn't have spread to the American mainland in any big way, therefore it's not a question worth wasting time over.

Ignoring Pearl Harbor and the Aleutian Islands, of course...

That would require one of the major enemies of the United States to have had the ability to construct a navy at least as powerful as that of the United States by the end of the war. Fortunately, none of our enemies had anywhere near that kind of power - Japan couldn't come close to competing, and they had much more naval construction capacity than Germany.

Either that, or Mexico would have had to join the Axis and go to war with the United States, but they'd have to have been monumentally stupid in a scale that is difficult to fathom.

What if bullfrogs had wings? They wouldn't bump their butts after they jump.

None of the Axis powers had the capability to get to North America, and if any had tried, their logistic chain would have been so long and tenuous that it would have been throwing troops away. That would have shortened the war, and had no substantive effect on the US otherwise.

I think you probably would have found that it was OK for the Nazis to wreak so much havoc in Europe, but to have attempted this in the United States is a different matter altogether. I'm European myself, but will not believe for one second that any attempt by the Nazis to harass Americans on their own soil being so heavily armed on a individual basis (as per head of population) would have got them very far, let stand if anything like this would happen today.

The only reason America is so powerful today is because they stripped Britain of all its money and made them pay for every last bit of money that the Americans lended. If the war was fought on american soil, then maybe they would have realised that they needed to do something a bit quicker, and they could've ended the war faster. Also, they wouldn't have been the greedy country they are now because they would have had to pay for the war damage etc for their own country.

It wouldn't hurt us as bad but we would definitely be a bit behind technologically.

Interesting question.