To what extent did US entry into the First World War contribute to Allied victory?

The question requires that candidates consider how far the entry of the US into the First World War contributed to the Allied victory. They may identify a range of factors that support the view that US entry was a major factor in Allied victory. Some may propose an alternative thesis and argue that other factors were more important, for example the overwhelming strength in numbers of the Allied forces, especially following the entry of Italian forces in 1915 and the impact of British Imperial and dominion forces. Economic factors, including the blockade, the failed war economy in Germany, the weakness of German allies and the domestic instability within the Central Powers, may also be considered. Nevertheless, the bulk of the response must deal with the significance or otherwise of US entry into the war.