There are a couple of ways I can answer this question. The Allied Powers were called the Allies in World War I and War II. In World War I, this included Great Britain, France, the Soviet Union, Italy, and the United States. The Allies Powers in World War I formed from the Triple Entente that existed prior to the war. The Triple Entente included Great Britain, France, and the Soviet Union. This alliance existed to counter the Triple Alliance of Germany, Austria-Hungary, and Italy. In World War II, the Allies included France, Great Britain, France, and the Soviet Union.
Another way to look at this question is to consider how the Allies got many of their supplies in World War II. The United States was called the “arsenal for democracy” in World War II. We provided many of the materials that the Allies needed to fight the Axis Powers in the war. After Germany and Italy overran much of Western Europe, the Allies had a major supply shortage. We provided the Allies with many supplies before we joined World War II as well as after we entered World War II.