Or during the 1930s, the Soviets are more involved in conflicts (for example with Japan, or in Spanish War, or both) than IOTL and are successful, maybe they win quicker and easier in the Winter War as well, and the Purges are avoided or reduced (or at least not known abroad). So, Soviet Union looks like the military great power it actually was, and Germans abandon the idea of Barbarossa, which just became obvious suicide. Hitler may or may not accept it easily. On one hand, Barbarossa was his obsession. On the other hand, his main goal was to get glory and power for himself, and he did make a number of rational decisions (when not blinded by hubris), so if the Soviets really look (and are) too strong and German military leaders strongly oppose any war in the east, I can see Hitler turning his ambitions towards the British Empire (a "nation of shopkeepers") instead.