Tripartite Pact
The Tripartite Pact, also known as the Berlin Pact, was an agreement between Germany, Italy and Japan signed in Berlin on 27 September 1940 by, respectively, Adolf Hitler, Galeazzo Ciano and Saburō Kurusu. It was a defensive military alliance that was eventually joined by Hungary (20 November 1940), Romania (23 November 1940), Bulgaria (1 March 1941) and Yugoslavia (25 March 1941), as well as by the German client state of Slovakia (24 November 1940). Yugoslavia's adherence provoked a coup d'état in Belgrade, and Italy and Germany responded by invading Yugoslavia (with Bulgarian, Hungarian and Romanian assistance) and partitioning the country. The resulting Italo-German client state of Croatia joined the pact on 15 June 1941.
The Tripartite Pact was directed primarily at the United States. Its practical effects were limited, since the Italo-German and Japanese operational theatres were on opposite sides of the world and the high contracting powers had disparate strategic interests. Some technical cooperation was carried out, and the Japanese declaration of war on the United States propelled, although it did not require, a similar declaration of war from all the other signatories of the Tripartite Pact.