What was the “war guilt” clause in the treaty of versailles?

Article 231 of the Treaty of Versailles - known as the War Guilt Clause- stated that Germany was responsible for starting WWI.  It was added as an exchange with France and Belgium to reduce the amount of money Germany would pay in reparations to compensate for war damages.  In the end, it was the one article the stung the most for Germans who did not feel that they were solely responsible for the start of the war.  It stung to the Weimar leaders who tried to meet all the terms of the agreement.