So why did the dream team collapse? Too many arguments about what kind of mustache was better? Probably, but there were two other problems. First, they couldn't agree on how to divide the big Risk board that is Earth, with Bulgaria, Iraq, and Iran being particular sticking points. That might have been resolved -- what's a little Bulgaria between supervillains? -- but Hitler had a huge hate-on for the Soviet Union that simply would not go down.
The German ambassador to Moscow told Berlin that an invasion would end in disaster, and that Stalin seemed willing to meet whatever economic demands Hitler made, so long as war was avoided. The German foreign minister and other pragmatic high-ranking Nazis were so strongly in favor of cutting a deal that they even conducted talks behind Hitler's back. They saw Britain as the true enemy, and feared that opening a two-front war would be their doom (spoiler: they were right).
For his part, Stalin seemed content to sit on the sidelines and watch Churchill and Hitler tear each other apart. But Hitler thought that the guy who was sending him free food was a jerk (pot, kettle, black, etc.), so lil half-stache responded with a giant middle finger and an invasion. If someone had been able to talk some sense into Hitler, the whole war could have turned out differently (uh ... probably worse). Although any scenario that involves talking sense into Hitler is admittedly a stretch.