What countries made up the allied powers in ww1?

 The main powers of the Allies in World War I were Great Britain, France, and Russia, along with Japan and Italy.  The United States also later joined the war with the Allies.

Context/explanation:

The military plans laid before World War I presupposed a major war between countries, and the nations of Europe joined together in competing alliances.  The Triple Entente had Britain, France and Russia as allies -- and those nations became known as the Allies in the Great War (now known as World War I).  Japan joined the Allies in hopes of obtaining German territories in the Pacific.  Italy, which had been in a secret alliance with Germany prior to the war, change its loyalty and sided with the Allies beginning in 1915.  It wanted Italian-population lands that were controlled by Austria.

The United States entered the war on the side of the Allies in 1917.