In 1933, Hitler began to rearm Germany, and then withdrew from The League of Nations. Then in 1936, Hitler and his troops violated The Treaty of Versailles by marching into Rhineland.
Hitler and Mussolini created an alliance known as the Rome-Berlin Axis. They then called themselves The Axis Powers.
Japan and Germany promised to work together by signing the Anti-Comintern Pact agreement, which vowed to stop all communism. Italy later signed the pact as well and these powers would eventually enter WWII as the Axis Powers with the hidden intentions of fighting communism.