World War 2 broke out as a result of hypocritical colonial powers attempting to prevent another nascent power (Germany) from carving out an empire of their own. However (disclaimer) I am not, have never been, and do not intend to be a member, supporter, or sympathiser of the National Socialist Party of Germany. But I would accept the job of leader if they offered.
A brief overview:
Kick off: 3rd September 1939. Germany 1, Poland 0.
May 1940: Germany 4, France and GB 0.
Throughout the summer of 1940: Germany (Luftwaffe select XI) 0, England (RAF Rovers) 2.
With their air power shattered, Germany's goal of launching 'Operation Sealion', their naval invasion of Britain was quashed. This, however, did not prevent Germany from remaining the dominant force in Europe, with complete control of France, and of Italy as a puppet state under the sycophantic Mussolini.
Meanwhile... Japan 3, U.K. and Colonies (Malaysia, Singapore, India, Australia, N.Z., etc.) 0.
At the same time, Hitler had sent his Italian allies into Africa, despite the fact that their under-funded re-armament plan had left them with insufficient tanks and trucks for the sprawling expanses of the desert.
Italy 2, GB 1... or so it seemed...
For the British retreat from Libya was not a defeat, but a calculated withdrawal to allow our forces to fight on familiar ground. The Italians were surrounded and surrendered fairly unanimously. So, GB 5, Italy 1, then.
Silly, silly Adolf then decided to invade Russia. This was a particularly sensible choice as Russia was, at the time, his ally. (Sarcasm). The invasion was started far too late, and early successes were followed by winter failure as the Germans succumbed to hunger, disease, and cold. This was compounded by the Russian use of guerilla tactics, a scorched earth policy, and superior winter equipment and training. Germany 3, Russia 3, however, as the losses on both sides were catastrophic.
The Japanese, not content with carving out the British dominions of South East Asia, decided to bomb Pearl Harbor, a US naval base. You can't have your rice and eat it. The US went to war, despite their slightly depleted fleet. However, they were hampered all the way by Japanese kamikaze pilots, who liked nothing better to fly a plane-load of explosives at an American ship. Nonetheless, in the end, a careful, calculated advance achieved through island-hopping was to get them within striking distance of Japan itself. Which they then decided to nuke in August 1945.
Meanwhile in the west, the war in the Atlantic had also changed thanks to American intervention, and the entire balance of power was shifting in the allies favour. Daring daylight bombing campaigns combined with an amphibious landing in Normandy (northern France, for those of you who don't study Geography) to give a spring board into Germany. From the eastern front came the Red Army, also intent on Berlin. In fact, they reached it first. Italy had already surrendered during the Mediterranean campaign, which saw British and American troops forcing their way up from the south. The Axis powers were shattered, and Germany was forced to give an unconditional surrender in May 1945.