I often hear it said that the USA joining the war was one of the largest factors that led to the wars ending, however during my reading of 1914-1918 by David Stevenson he seems to indicate that American forces were an ineffective fighting unit, mostly due to the fact the soldiers and officers were inexperienced in trench warfare and favoured frontal attacks that had been abandoned by the other Entente powers. Was the true impact of the USA joining more to do with provision of supplies or were they actually influential in battle?
When US forces first arrived on the Western Front, they were inexperienced and few in number. The first few times they saw combat were as units attached to non-US forces, and their impact was minor.
However, they were going to gain experience over time, and the arrival of about 2 divisions per week (and US divisions were big) would quickly make them far-from-few in number. Essentially, US entry into the war meant that the Allies were going to win the war if it continued as a battle of attrition, despite German forces freed by the defeat of Russia. The prospect of certain victory in the not-too-distant future improved Allied morale.
The only chance the Germans had of victory was to avoid that battle of attrition, which meant winning ASAP, which meant going onto the offensive. Thus, the German 1918 Spring Offensive (Kaiserschlacht) was launched while the Germans still had numerical superiority. This failed to defeat the Allies, and made quite a few Allied generals gleeful, as it meant that they could fight the Germans in the open or in hasty defences, rather than attacking very strong defensive positions. During the offensive, German numerical superiority was reversed
by the combination of German losses and the continuing arrival of more US forces, and the Germans were left in weaker positions along a longer front.
By the end of the German offensive, US forces were no longer inexperienced nor few. They had already won (small) battles under US command, The US had the experience and numbers to play an important role in the last three months of the war, the Hundred Days Offensive which crushed the Germans on the Western Front.
Had the Western Front remained a war of attrition, the US entry would have brought victory, but it would have been well into 1919 (or later!). Provoking the 1918 Offensive meant that the war finished in 1918, a far-from-insignificant impact on the war.
