The Tripartite Pact, also called the Three-Power Pact, was signed in Berlin on September 27, 1940 by representatives of Nazi-Germany, Italy and Japan. The agreement formalized the Axis Powers' partnership, and can be read as a warning the USA to remain neutral in World War II - or become involved in a war on two fronts.
In the pact the three nations agreed that for the next ten years they would
The Tripatrite Pact was subsequently joined by Hungary (November 20th, 1940) and Romania (November 23rd, 1940). Bulgaria joined on March 1st, 1941, prior to the arrival of German troops.
On March 25th, 1941, Prince Paul (Pavle), Regent of Yugoslavia, signed the Tripartite Pact. It was not easy for Hitler to gain Yugoslavia's cooperation. There were strong anti-German feelings in the country, especially among the Serbian population. March 27th the regime was overthrown by a military coup d'état with British support, and the 18 years old King Peter II of Yugoslavia seized power.
Although the new rulers opposed Nazi-Germany, they also feared that if Hitler attacked Yugoslavia, Britain was not in any real position to help. For the safety of the country, they declared that Yugoslavia would adhere to the Tripartite Pact.
Postponing Operation Barbarossa the Germans simultaneously attacked Yugoslavia and Greece. From April 6th, Luftwaffe pounded Belgrade to the ground for three days and three nights. German ground troops moved in, and Yugoslavia capitulated on April 17th.
German declaration of war
On December 7th, Japan attacked the United States' naval bases at Pearl Harbor. According to the stipulation of the Tripartite Pact, Nazi-Germany was required to come to the defense of her allies only if they were attacked. Since Japan had made the first move and attacked, Germany was not obligated to aid. On December 11th, Hitler entered the Reichstag to formally declare war on the United States, thus quenching that US opinion which opposed USA's engagement against the Third Reich.