What can we conclude from the Second World War?
The most important thing that we can conclude from World War II is that modern wars are won by industrial capacity. In WWII, the Allies started the war in a very disadvantageous military position. The Germans and the Japanese appeared to be militarily superior to all Allied countries. However, the Allies were still able to win the war, largely because of the industrial capacity of the United States.
A second conclusion is that wars of that era were affected tremendously by geography. The English Channel prevented the invasion of England. The location of the United States prevented it from coming under any serious attacks that would have degraded its industrial capacity. The expanse of the Soviet Union allowed it to absorb the German invasion.
The war ended in the summer of 1945 it is estimated that 50 million people lost there lives. It ended with the unconditional surrender of the axis power. Germany surrendered on may the 5th to the western allies and on may the Th to the soviet union about a week after Adolf Hitler committed suicide. Japan was to hold out for another few months and was preparing desperate and bloody Defence in the event of an American invasion of islands.
Never, never, ever again... please.