The major Allied Powers were Britain, France, Russia, and the United States. The Allies formed mostly as a defense against the attacks of the Axis Powers. The original members of the Allies included Great Britain, France and Poland. When Germany invaded Poland, Great Britain and France declared war on Germany. - Ducksters.com
Explanation:
All were part of the Allied Powers except for teh U.S who joined in 1917. The major Allied powers in World War I were Great Britain (and the British Empire), France, and the Russian Empire, formally linked by the Treaty of London of September 5, 1914. Other countries that had been, or came to be, allied by treaty to one or more of those powers were also called Allies: Portugal and Japan by treaty with Britain; Italy by the Treaty of London of April 26, 1915, with all three powers. Other countries—including the United States after its entry on April 6, 1917—that were arrayed against the Central Powers were called “Associated Powers,” not Allied powers; U.S. -https://www.britannica.com/topic/Allied-Powers-international-alliance