Following the ratification of article 231 of the Treaty of Versailles at the conclusion of World War I, the Central Powers were made to give war reparations to the Allied Powers. Each of the defeated powers was required to make payments in either cash or kind. Because of the financial situation in Austria, Hungary, and Turkey after the war, few to no reparations were paid and the requirements for reparations were cancelled. Bulgaria, having paid only a fraction of what was required, saw its reparation figure reduced and then cancelled. Historians have recognized the German requirement to pay reparations as the "chief battleground of the post-war era" and "the focus of the power struggle between France and Germany over whether the Versailles Treaty was to be enforced or revised." The Treaty of Versailles (signed in 1919) and the 1921 London Schedule of Payments required Germany to pay 132 billion gold marks [all values are contemporary, unless otherwise stated]) in reparations to cover civilian damage caused during the war. This figure was divided into three categories of bonds: A, B, and C. Of these, Germany was required to pay towards 'A' and 'B' bonds totaling 50 billion marks () unconditionally. The payment of the remaining 'C' bonds was interest free and contingent on the Weimar Republic's ability to pay, as was to be assessed by an Allied committee. Due to the lack of reparation payments by Germany, France occupied the Ruhr in 1923 to enforce payments, causing an international crisis that resulted in the implementation of the Dawes Plan in 1924. This plan outlined a new payment method and raised international loans to help Germany to meet its reparation commitments. Despite this, by 1928 Germany called for a new payment plan, resulting in the Young Plan that established the German reparation requirements at 112 billion marks () and created a schedule of payments that would see Germany complete payments by 1988. With the collapse of the German economy in 1931, reparations were suspended for a year and in 1932 during the Lausanne Conference they were cancelled altogether. Between 1919 and 1932, Germany paid less than 21 billion marks in reparations. The German people saw reparations as a national humiliation; the German Government worked to undermine the validity of the Treaty of Versailles and the requirement to pay. British economist John Maynard Keynes called the treaty a Carthaginian peace that would economically