Stalin .
Benito Mussolini
Italy was a member of the Tripl Alliance, which formed into the main nations of the Central Powers when war broke out. It joined the war on the Allied Side.
In world war 1 the central powers were Germany, Austria-Hungary and the Ottoman empire. Italy was part of that alliance but because it switched sides before the name changed from the triple alliance to the central powers it is generally not considered a central power. The allied powers were the British empire, France, Russia and later the United states.
Initially they did not come to an agreement with Russia because Russia had allied with Germany. Russia was attacked and changed their alliance with the Allied Forces. So they became part of the Big Three: US, USSR and UK.
The main powers of the Triple Entente (the Allied Powers) in World War I were France, Britain and Russia. Italy initially sided with the Triple Alliance (Austro-Hungary, and Germany), but turned away and sided with the Triple Entente.
alliance
The Allied Forces.
There were called the Allied Force, The Allies, an ally or the alliance.
Italy
The Allied Forces
The word "alliance" comes to mind. The allied countries are known as allies.
Italy was a member of the Triple Alliance with Germany and Austria-Hungary. Italy refused to join the war as a member of the Central Powers citing she was to aid Germany if attacked by France.