USS Shaw (DD-373) in the context of Battle star

The causes of World War II have been given considerable attention by historians. The immediate precipitating event was the invasion of Poland by Nazi Germany on September 1, 1939, and the subsequent declarations of war on Germany made by Britain and France, but many other prior events have been suggested as ultimate causes. Primary themes in historical analysis of the war's origins include the political takeover of Germany in 1933 by Adolf Hitler and the Nazi Party; Japanese militarism against China, which led to the Japanese invasion of Manchuria and the Second Sino-Japanese War; Italian aggression against Ethiopia, which led to the Second Italo-Ethiopian War; or military uprising in Spain, which led to the Spanish Civil War.

During the interwar period, deep anger arose in the Weimar Republic over the conditions of the 1919 Treaty of Versailles, which punished Germany for its role in World War I with heavy financial reparations and severe limitations on its military that were intended to prevent it from becoming a military power again. The demilitarisation of the Rhineland, the prohibition of German unification with Austria, and the loss of its overseas colonies as well as some 12% of the pre-war land area and population of the metropole all provoked strong currents of revanchism in German politics.