Tripartite Pact

The Tripartite Pact, also called the Three-Power Pact, Axis Pact, Three-way Pact, or Tripartite Treaty was a pact signed in Berlin, Germany, on September 27, 1940, which set up the Axis Powers of World War II. On that date, it was signed by three countries: Germany, Italy, and Japan. 
The pact was later joined by Hungary (November 20, 1940), Romania (November 23, 1940), Slovakia (November 24, 1940), Bulgaria (March 1, 1941), Yugoslavia (March 25, 1941) and Croatia (April 10, 1941). Japan included some countries that were under its control.
The countries that signed the pact agreed to give ten years of political, economic, and military help to one another. Also, if any country that signed the pact was attacked by another other country that had not joined the war, such as the United States or the Soviet Union, all of the other countries in the pact countries would declare war and help.
In 1943, the pact began to fall. Many countries had ended the war or joined the Allies. Although the pact remained in effect until Japan's surrender in August 1945, Germany's surrender three months earlier had made the pact meaningless.