Another key factor to the stalemate breaking was the American Entry into the war. Since the beginning of the war, America had been on the side of the Allies, providing them with vital supplies which could not be accessed due to the war. Due to this large dependence on shipping from America, the Germans sent many U-boats and submarines to the Atlantic to sink these ships, and eventually began a policy of unrestricted submarine warfare, which meant that the German ships would attack any ship, Allied or neutral, merchant or military. Inevitably, this led to passenger ships being sunk and on 15th May 1915, the German submarine U20 sunk the Lusitania off the coast of Ireland, which caused the deaths of thousands of passengers; hundreds of which were American. This greatly infuriated the American people. When news was leaked to the press that Germany had sent a telegram asking Mexico to declare war on the U.S.A, this angered America even more. Contrary to its previous policy of isolationism, the general consensus was that the Americans wanted to join the war, and on April 6th 1917, the U.S.A declared war on Germany. The American Expeditionary Force (A.E.F), commanded by General John Pershing was sent to Europe to fight for the Allies; this force had grown to almost 2 million men by the end of the war. However, Pershing had calculated that 3 million soldiers would be needed, 1 million of which would be needed within a year. However, the first battle that the Americans took part in was at the village of Cantigny, in May 1918, over a year after they had entered the war. The battle was a success and the village was captured, but there were only 163 fatal casualties. The British and the French insisted that the Americans had to shoulder a greater burden of the war, but Pershing thought differently. Horrified by Allied leadership, he did not want to entrust his soldiers to the Allied generals, and wanted American autonomy; he insisted that the American forces act independently, which greatly irritated the Allied generals. However, by the end of the war, there had been over 300'000 American casualties.
Since the beginning of the war, Britain had set up a naval blockade to prevent Germany from shipping in its vital supplies, which was part of the strategy of attrition. The only access to the sea that Germany has for shipping purposes was the North Sea, and Britain was eager to make sure Germany could not import the vital supplies that she needed not only for the military needs of the country, but also for the everyday supplies which were being drained by the war effort, e.g. food. A minefield was placed all along the North Sea between Britain and Norway, to prevent Germany from sending any ships through it. 75 U-boats were sunk due to the placement of mines. As soon as war was declared in 1914, Allied ships prevented other vessels from entering German ports, and all ships going through neutral ports, such as Rotterdam, were thoroughly searched for any contraband material. Also, a lot of staple supplies, such as wheat and timber had been imported from Russia before the war; now this obviously no longer available. Due to this lack of foodstuffs, the German people suffered greatly, especially during the great 'Turnip Winter' of 1916-1917. 'Ersatz' food was also produced as a result; poor substitutes for food no longer available, such as clover flour. Apart from the looming spectre of starvation, other problems threatened Germany as well; many workers observed the Russian Bolshevik revolution of 1917 and in early 1918, there were several revolts across German industrial areas. Also, the Spanish Influenza Epidemic struck and killed thousands of Germans; this can be attributed to the poor diet of the German people. By 1918, starvation had claimed the lives of nearly 300'000 people in Germany. Due to this, morale was very low on the German Home Front and the German leaders knew that a gamble had to be made, else the German people would revolt, possibly even following the example of the Russians in November 1917.
The last main factor which contributed to the breaking of the stalemate on the Western Front was the German Spring Offensive of 1918. 62 experienced divisions with high morale became available after the surrender of Russia in the winter of 1917, and so were quickly transported to the Western Front. This was just the thing that the Germans needed if they were ever to break through the stalemate on the Western Front and knock France out of the war before the arrival of millions of American soldiers could made a German victory impossible. This is why General Erich Ludendorff, the man in charge of the entire operation (which was codenamed 'Michael') decided to strike at the point where the French and British troops met. If the French troops were separated from the British troops, there would be a strong likelihood that France would surrender, and France could be captured. And so, trained in brand new tactics, Operation Michael began on March 21st. The operation was a success; German forces advanced up to 40 miles. However, the old problem still arose; German forces were not able to hold their gains. To form the new assault divisions, the best men and officers had been taken from each division; this left the ordinary divisions less capable, or in Gary Sheffield's words 'squeezed lemons'. Indeed, the assault divisions made astounding progress, but at a high cost, and the elite troops forming these divisions were irreplaceable in terms of experience. It was not only due to the fact that initial gains could not be held effectively, but of the mediocre planning of the long-term strategy for the offensive. Since the British troops were able to hold on to some key points, the direction of the offensive was changed to where it would be most tactically successful. Eventually, the divisions became undisciplined and were looting Allied supply dumps; morale was low due to high casualties, and the troops were exhausted because of constant action; there was no longer the rotation of forces which allowed forces to stay in the support trenches for a while. The Spring Offensive led to the breaking of the stalemate not only in the short-term, but up until the end of the war; after the German troops had broken through but failed to meet their objectives, the Allied 'Hundred days' counter-attack continued to push the Germans back until the armistice was signed.
It is important to remember that none of these factors individually contributed to the stalemate being broken in 1918, but that they were all inter-related, i.e. they all affected each other in many ways. The Spring Offensive took place mainly because of the other three factors: the American entry into the war meant that a gamble had to be taken by the Germans to capture France before the Americans could arrive in huge numbers, and the pressure in Germany due to lack of materials meant that an offensive had to be made not only as a gamble, but to boost morale back in Germany. The blockade led to the Germans beginning a policy of unrestricted submarine warfare in the Atlantic Ocean, which then led to the sinking of the Lusitania, which was a major contributing factor to the American entry into the war. However, the main reason that the stalemate broke was due to the Spring Offensive of 1918; the other factors were the reasons this offensive took place. The American entry into the war created pressure on the German generals, as did the shipping blockade, but the improvements in technology made the idea of a grand offensive seem better. It is also important to remember that another major factor contributing to the Spring Offensive, and therefore the breaking of a stalemate, was the Russian Revolution of 1917, which led to the Russian surrender and the freeing-up of 62 divisions. Without these divisions, Germany would never have had the experienced manpower to operate all the new technology it had developed and so the Spring Offensive could never have happened.
In conclusion, the actual main (and therefore the most important) factor contributing to the breaking of stalemate on the western front was the German offensive of 1918; however, this could not have happened without the other factors taking place as well, which makes them all very important factors also.
