Germany is generally given blame for starting the war. However the causes are much more involved than simply blaming 'German aggression'. Hitler said the war was one between the 'have's and have nots'. By this he meant that the club of nations that had empires - Britain, France, Russia and the USA were the have's. The nations that desired empires or were trying to expand their limited ones were Italy, Germany and Japan. The desire of the 'have's' to hang on to their wealth, influence and world dominance clashed with the desire of the 'have nots' to obtain some of those assets for themselves. Japan and Italy were aggressively increasing their empires many years before Germany started expansion. German power was exercised years later but due to greater German military ability, their results were most impressive. Specific events are often shown in history books as the 'start' of WWII such as the German invasion of Poland in Sept 1939 or Pearl Harbor in Dec 1941. With these specific dates it is thus easier to categorize who is to 'blame' for the war - Germany in Poland and Japan in Asia. Such simplistic overviews however, hide the root causes of war - the desire of all nations for economic expansion and cultural dominance of their neighbors.
Germany
Japan
Germany
This is an opinion type question, of course. Who is to blame on how the war startedwill be different from the blame for why it was not stopped or on how the war was fought. Most historians would say that no one country was entirely to blame for the First World War. Actually most people that participated in the war would say that the cause of the start of the war was complicated and that several countries were to blame. Now after the war started, Germany's decisions can be questioned. Germany, as the military aggressor on the Western Front, could have ended the war years sooner, but it didn't. Germany can be blamed for many things, including invading neutral countries and sinking neutral ships.
The Germans were to blame
The Jews.
Austria-Hungary placed impossible demands on Serbia.
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Serbia
It depends on which war. If you are asking about World War 1, I would say no. I think Austria-Hungary should get most of the blame. In World War 2, I would say Germany was to blame, but I will also add that other countries were headed for war anyway regardless of anything that Germany did.
Germany was largely blamed for World War 1. The Treaty of Versailles, signed in 1919, placed full responsibility for the war on Germany and its allies and imposed large reparations on them. This blame contributed to the political and economic instability in Germany during the post-war period.
Germany was forced to take all the blame for World War I as dictated in the Treaty of Versailles.