What makes you say they almost won? They certainly did not. They could’ve taken Moscow and it would’ve made no difference. The USSR had way too many people, people who really didn’t want to be taken over by Nazis, and way too many resources from the US/UK for Germany to overpower them. And Germany was doing extremely poorly on resources (especially oil and steel) even by 1940– the entire reason they invaded the USSR to begin with was because they didn’t have enough oil to meet their demands and they would collapse without seizing the USSR’s oil reserves. The British cutting them off from North African oil made the issue signicantly more urgent.

Germany practically signed their own death warrant the moment they invaded France. They just didn’t have the resources or arguable even the manpower to sustain that kind of war, even when controlling most of Europe outside of the USSR and a large portion of Africa.

I’ll give some numbers to help visualize: During WW2, Germany’s peak oil production was 71,000 barrels per day (1944), mostly synthetic oil from coal. For comparison, the United States’ peak oil production was 1,875,000 barrels per day (1944) and the USSR’s was 700,000 barrels per day (1941). Germany’s peak steel production was 29.3 million tons (1944); the United States’ was 89.6 million tons (1944). The USSR produced less, about 8.5 million tons at peak (1943), but they also received about 400,000 jeeps, 7,000 tanks, 5,000 other armored vehicles, 12,000 aircraft, and a bunch of other supplies totaling up to about USD$150 billion injusted for inflation, so steel wasn’t really much of an issue. Comparing populations, Germany’s was 69 million. The US’ was 132 million and the USSR’s was 190 million.

Considering that, it may become easier to see why Germany had absolutely no chance in the long-run, even in a hypothetical (impossible) scenario where they only fought either the USSR or the US.