The Allied forces were opposed to the the Central Powers. (Germany, Ottoman Empire, Austro- Hungarian Empire). The major guys that made the Allied powers were the British Empire, France and the Russian Empire. These nations had joined together from treaties made years before the war, promising to help each other if any of them were attacked. As the war progressed more countries joined the Allies including the USA.
The Allies were victorious in the end, and dictated the fate of the Central Powers future.