What was a major consequence of American entry into WW1?

The entry of the United States into World War I had a significant impact on the morale of the Allies, which is why this choice is considered the correct answer. Prior to America's involvement, the Allies faced numerous challenges including dwindling resources, war fatigue, and the ongoing stalemate on the Western Front. The arrival of American troops and supplies brought a much-needed boost, both materially and psychologically, to Allied forces. It signified that a powerful and fresh military was joining the fight, which revitalized their efforts and gave them confidence in achieving victory.

The notion of increased global trade, while relevant during wartime, was more associated with the economic effects of the war rather than a direct consequence of U.S. entry into it. New territorial acquisitions were not a direct result of America’s involvement, as the immediate goal was to support the Allies and restore balance rather than expand territory. The shift from isolationism does relate to a longer-term change in U.S. foreign policy, but the immediate consequence that most notably impacted the dynamics of World War I was indeed the boost to Allied morale.