By December 1916 - the Entente Powers knew that they would win. German losses could not be sustained, that was the bitter truth that Falkenhayn's failed attempts at attrition proved throughout 1916. After November 1916 the German Army on the Western Front went onto the defensive and even then British and French bite-and-hold assaults kept them moving back. It was only the collapse of Russia and it's withdrawal from the war that allowed the Germans to make one last desperate effort in 1918. That attack through a series of five offensives failed for exactly the same reasons their initial attack in 1914 failed and then within 21 days of the last of those offensives petering out the British, French and American Armies went over onto the offensive - 100 days later the First World War was over. British leaders Lloyd George and Churchill thought that the Entente powers would have to wait until 1919 to defeat the Germans, Haig proved them wrong, the tactics developed from 1916 and 1917 were refined and put into effect as the Germans ran out of steam and once the offensive started there was never going to be any chance of the Germans stopping it.