The Second World War

The Treaty of Versaille was harsh on Germany, it depended on the goodwill of the Germans to comply which they did until there economy collapsed and their internal politics (NAZI's & Communists) used the Treaty to bludgeon the Weimar Republic and solicit support from an increasingly desperate and hostile German people. When parts of the Treaty were tested and Germany found that no one would do anything, then completely breaking the Treaty became part of the German ethos.
Critical to the collapse of the Treaty was the non-participation of the US in the League of Nations and their economic support of Germany.

USA was suffering at the hands of Japan. 

i. Hitler declared openly that he would not abide by the Treaty of Versailles.
ii. Hitler had imperialist designs and wanted to establish the rule of the Swastik over the world.
iii. He also concluded the Non-aggression Pact with Russia. 
iv. Hitler also started group- formation of his own. He concluded an Anglo-German Naval Agreement in 1933 A.D.

i. Two atom bombs were dropped on its cities i.e. Hiroshima and Nagasaki. The cities continued to reel under the radiations effects of this nuclear weapons.

ii. Vast areas of land were rendered unworthy of cultivation and human habitation.