The war-guilt clause of the Versailles Treaty was a very controversial one. It basically said Germany was responsible for World War I and all of the events that happened during the war. The Germans resented this tremendously. The Germans said it was Austria-Hungary that declared war on Serbia, starting World War I. The Allies believed that since Germany agreed to support Austria-Hungary that Germany was, therefore, responsible for the start of World War I. The Allies believed Germany could have prevented the war by not agreeing to support Austria-Hungary if Austria-Hungary declared war on Serbia. The anger this caused in Germany was one of the factors that led to the rise of Hitler to power.
In return for this statement being added to the Versailles Treaty, the Germans would pay less money in damages to the Allies. Even with a reduced reparations amount, Germany was still burdened with heavy reparations that ultimately caused its economy to collapse, leading to the rise to power of Adolf Hitler and the Nazi Party.