If Hitler had never invaded the USSR, there would be no war in Europe. The United Kingdom may have survived the war if Germany had not invaded the USSR. The Soviet Union likely would have collapsed and there would have been a major power vacuum in Eastern Europe and Asia. Japan may have eventually succeeded in invading China instead of being defeated by the US, which could have meant a major difference for Western Europe's culture, economy and politics following World War II.
If Hitler never invaded the USSR then Italy may not have allied with Germany's Axis Powers, meaning that Italy might not even exist as a country today. Naples might be an independent city-state ruled from Rome instead of an Italian province ruled from Rome or Milan.
