If you had the UK USA France, and Russia/USSR against you, you were fucked. Same applied to world war 1.
These people were building like an entire fucking ship per day. They averaged almost one whole aircraft carrier per month. Germany was running their cars on wood gas. Absolutely no chance. Would have been more costly in terms of casualties without the USSR, but 1940s USA was unbeatable, especially with their untouchable production base
How can they "spend more" than the US? They were literally given materiel and money by the US. The money the USSR spent was from the West.
The European war was fought with Russian troops, British intelligence, and American money. Also, there was an entire other war in the Pacific that the US fought at the same time. It's not possible for the Soviets to have spent more, just based on that fact alone.
Lend-Lease was absolutely important when it came to specific material (e.g. trucks, aviation fuel).
But in total numbers it was still only 4% of Soviet War production.
I don't know who spent more money in the war (and it is irrelevant really when you look at dozens of millions of deaths), but Lend-Lease alone does not answer that question.
The Soviets could not have won without the Lend Lease, even Stalin admitted this.
Of course, if Stalin hadn't murdered half of their officers and had an icepick put in the brains of the guy who built the Red Army in the first place it might have been a different story.
America had an incredibly privileged strategic position compared to the Axis, and didn't share a land border with any of them.
The fears of an Axis invasion were simply impossible. The US Pacific fleet matched the Japanese and the Atlantic was stronger than Italy and Germany combined at the start of the war, just counting battleships and screens and ignoring that America was already moving towards a carrier based fleet unlike both of them. There is no world in which America falls to a naval invasion before it had time to mobilize.
And, unlike the Axis, America was and is the world's largest oil producer. It could afford to run its Navy day and night.
The only way the the Axis wins this hypothetical is if America was alone because it went full non-interventionist (like the Republican party wanted) and the Axis conquered the rest of the world first.
That all said, these circumstances would almost certainly lead to a stalemate rather than Axis capitulation. The Axis navies get destroyed (again), but America probably wouldn't be willing to pay the blood price to invade them, and the Manhattan Project was unlikely to succeed without the contributions of non-Americans.
From the American perspective, however, a stalemate is a victory. It's a defensive war and the goal is survival, not conquest.
Tl;Dr Stalin himself made a solo victory (survival) impossible for the USSR, the US Navy and the freaking Pacific and Atlantic Oceans made it impossible for America to lose.
Meh. Don't get me wrong, the USA joining world war 1 was the final nail in the coffin and likely cut the war short by a lot (and made it a slam dunk for the allies, instead of a pyrrhic victory), but compared to, say, Canada or Australia (not to mention the UK and Russia that both lost as much, if not more men than France) they basically didn't fight. They joined very early and were invaluable in holding french territories throughout the war, which is why they both suffered more losses than the USA even though their militaries (and populations) were way smaller.
Very true, it's how we crushed the Japanese, too. They were almost literally clearing neighborhoods for reclaimed metal and wood, converting entire towns into production facilities and even with that, they paled in comparison to the productive giant of the Goblino. Their zeroes might take 3 planes out of ours, and we would replace them three-fold and with more experienced pilots. They were forcing young pups into dilapidated old craft at the risk of great military disgrace to Kamikaze us because they knew they had no better options. The horrors we faced in the Pacific were truly abject, but it still would have been remarkable to be a wallflower back then and see the collective gusto that we managed to pull together, and all while still maintaining a perfectly functional economy with a massive swathe of our workforce overseas. I read somewhere that the US was using not more than 20% of our manufacturing capacity towards munitions and craft, and even then we were absolutely devastating the Axis.
Had the USSR capitulated to the Germans, there was a real risk that the UK would follow as the German war machine could refocus its efforts. India would likely have fallen soon after to the Japanese. At that point, the German production base, which was already heavily geared up, would have access to all the resources it could possibly need, and the US would have had serious trouble defeating them. It would be a race to the A-bomb and who could produce them the fastest most likely, although it's questionable how effective the weapon would be with a consolidated Luftwaffe without a continental power keeping them busy.
Without the British, intelligence efforts against Germany would have significant issues. It's possible that the USSR would capitulate due to this.
Without US lend-lease, the USSR would have capitulated as well, and with only the British standing against Germany hope would have been lost.
The German war machine was extremely powerful. It could not keep going forever of course, and in due time they would have failed. But had any major power not been in the war, Germany could likely have consolidated enough power to avoid successful invasions from overseas powers.