The "Axis Powers" is defined as the group of countries that signed the Tripartite Act in 1940, consisting of Germany, Italy and Japan. The term Axis Powers is sometimes broadened to include other countries that were allied with the Axis, including Bulgaria, Romania, Slovakia, Croatia, Hungary and Yugoslavia.
The Tripartite Act was signed in Berlin, Germany in 1940 and established the Axis Powers. Germany, Italy and Japan agreed to assist one another if attacked by other countries for the next 10 years. The Tripartite act was preceded in 1936 by the Anti-Comintern Pact, which was an anti-communism treaty between Germany and Japan. The goals of the axis powers were to exercise military hegemony over the world and to ally against the Soviet Union and communism.