The American refusal to accept a British blockade that tried to prevent American sales of food to the Central Powers was important in removing any last lingering British hopes. It ensured that the British signed the Treaty of Amsterdam in 1917 rather than trying to repeat their long resistance of the Napoleonic War. However, the war was actually won long before 1917.
The superiority of the German Army was very obvious in their defeat of the more numerous Russian armies at the Battle of Tannenburg. However, their ability to survive shocks that would have thrown the command of their opponents into complete confusion was perhaps best shown in the near simultaneous destruction of the British Expeditionary Force, BEF, and the French 5th Army. On the night of 19th-20th August the senior officer of the critical right wing of the German Army, General Karl von Bülow, suffered a heart attack. The news, coming after the loss of nerve of von Prittwitz in the East, seems to have precipitated the nervous collapse of his superior Helmuth von Moltke.
However, the German military machine ran on with surprisingly little disruption at an operational level on any of the fronts. General von Kluck was temporarily given command of both 1st and 2nd Armies and immediately ordered the 2nd Army to take over the 1st Army's position opposite the British while the 1st Army advanced west and then south-west. This left 2nd Army in an apparently dangerous position under attack from the 21st to 24th August from both the French 5th Army, attacking across the Sambre, and the BEF, which attacked across the Mons-Condé canal. However, the Anglo-French advance to the line Soignies - Gembloux did not break the 2nd Army or fulfil dreams of recapturing Brussels. Following the French defeat in the battle of the Ardennes and the appointment of von Falkenhayn as Chief of the General Staff, the German 3rd Army was belatedly ordered to attack west across the Meuse. From the 24th August, they advanced rapidly and caused Joffre, Lanrezac and French to agree that retreat was essential. However, it was already too late. Leading elements of the German 1st Army managed to reach Le Cateau on the 26th August just ahead of the retreating BEF and nothing stood between von Kluck and a junction with Hausen's 3rd Army between Hirson and Rocroi.