On September 27, 1940, the Axis powers were formed when Germany, Italy, and Japan become allies with the signing of the Tripartite Pact in Berlin. The Pact provided for mutual assistance should any of the signatories suffer attack by any nation not already involved in the war. This formalizing of the alliance was aimed directly at “neutral” America–designed to force the United States to think twice before venturing in on the side of the Allies.
