What proved to be the major stumbling block for germany in russia?

You're talking about World War II, right? Well, yeah, at one point Germany attempted to invade the Soviet Union (specifically during the Battle of Stalingrad.) But a major stumbling block was the weather in the Soviet Union; it was fiercely cold and German soldiers were starving and sick. Eventually, it became so cold that the German military retreated and Hitler's plans for "world domination" officially ended.