The correct answer is "Germany".
After the end of World War I., The winning side of the Allies decided to gather in Paris on June 1919 in order to negotiate how would the political landscape of Europe look like in the aftermath of the war.
The result of this convention was the signature of the "Treaty of Versailles". One of the most important provisions of this agreement was the increase of Germany to "accept the responsibility for all the loss and caused damage" during the war. This resulted in Germany having to pay substantial fees to the Entente Powers.