What was the main reason for the failure of peace in Europe in the 1930s?

Answer 1

The provisions of the Versailles Peace Treaty of 1919, drawn up (mostly) by the victorious French and British. American President Hoover had strongly warned against taking revenge on the Germans through the peace treaty, but his advice was largely ignored by the others. The provisions saddled Germany with enormous damage payments, it robbed Germany of the military manpower to restore order and establish a strong Government in its post-War turmoil, it gave away large parts of its territories and territorial posessions to others and through this combination crippled severely Germany's chances of political and economic recovery. The Great depression of 1929 came on top of all that, causing a runaway inflation that totally dissolved ordinary Germans' savings and pensions.

The result was a political and social climate in Germany fraught with resentment and anger towards the Allies in which scapegoats were easily sought and named, "Jewish worldwide capitalism" being prominent among them. This climate also made possible the rise of the Nazi party and of Adolf Hitler.