This essay goes into very high detail on what took place during the second world war

Many historians have traced the causes of World War II to problems left unsolved by World War I (1914-1918). World War I and the treaties that ended it also created new political and economic problems. Forceful leaders in several countries took advantage of these problems to seize power. The desire of dictators in Germany, Italy, and Japan to conquer additional territory brought them into conflict with the democratic nations. After World War I ended, representatives …

…prolong the peace until Britain and France were ready for war. The two leaders were mistaken on both counts. The failure of appeasement soon became clear. Hitler broke the Munich Agreement in March 1939 and seized the rest of Czechoslovakia. He thereby added Czechoslovakia's armed forces and industries to Germany's military might. In the months before World War II began, Germany's preparations for war moved ahead faster than did the military build-up of Britain and France.