From 1915 to 1917, the trench warfare on the western front produced remarkably few decisive results. The front line during this time didn't move more than a few miles either way with the exception of the German withdrawal to the Hindenburg line in March 1917, despite several massive and bloody offensives from both sides. This was mainly due to the nature of the war ?óÔé¼ÔÇ£ a war of attrition with modern weapons. In these circumstances it was almost always the defenders who had the advantage. It became clear to commanders on both sides quite early on in the war...
others which had an effect. The British naval blockade of the Baltic sea had cut of a large proportion of Germanys food and supplies. Without these Germany was not producing enough to feed its armies and its population. In 1917 it was estimated it would be less than a year until food ran out. This added to the desperation and confirmed that, for the Germans, time was not on their side. This is also important, and means even if the Americans hadn't joined the war Germany would still be facing a time constraint to win victory in the west.