The Tripartite Pact: Its Conclusion and Conditions of Implementation in 1940

France's defeat in 1940 placed new pressures on the European powers' colonial interests in Southeast Asia, while Japan sought greater scope for southward expansion. Against this background, the Tripartite Pact between Japan, Germany, and Italy linked the European war with expansion in East Asia. Cooperation among the three was intended to deter further American intervention, but it did not bring their strategic objectives and decisions about war into complete alignment.

On September 9 and 10, Japanese Foreign Minister Yōsuke Matsuoka met German special envoy Stahmer in Tokyo, with the German ambassador to Japan also present. The summary of the meetings principally records the German position: Germany was not then asking Japan to assist an attack on the British homeland, but wanted it to tie down the United States. Germany also offered to help improve Japanese-Soviet relations and discussed supplies of armaments and resources. The record also makes clear that Italy had not yet participated in this round of consultations, so the Tokyo talks were not a meeting at which the three foreign ministers jointly signed the pact.

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On September 27, 1940, German Foreign Minister Ribbentrop, Italian Foreign Minister Ciano, and Japanese Ambassador to Germany Saburō Kurusu signed the pact in Berlin. Its text contained six articles. Article VI provided that it took effect upon signature and remained valid for ten years from that date, with renewal negotiable before expiry at the request of any party. The signing date was thus also its expressly stipulated effective date; it did not await a subsequent exchange of ratifications.

Japan's domestic deliberations and subsequent ratification record are distinct matters. A summary of the Privy Council examining committee's proceedings on September 26 preserves questions about the clauses and preparations for war. In a telegram of October 21, American Ambassador to Japan Joseph Grew also reported that the emperor had ratified the pact on October 19 and that its Japanese text had appeared in the official gazette on October 21. These dates are specifically those reported by Grew at the time. Ratification and promulgation must not be substituted for the Berlin signing date, nor should they obscure the pact's own provision for immediate entry into force.

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Articles I and II reciprocally recognized German and Italian leadership in establishing a “new order” in Europe and Japanese leadership in so-called “Greater East Asia.” This constituted recognition by the three powers of one another's expansionist positions, not evidence that the peoples of the regions concerned consented to their domination. Article III further provided for political, economic, and military assistance, but under a specific condition: one of the parties had to be attacked by a power not then involved in either the European war or the Sino-Japanese War.

This condition did not impose an unrestricted obligation on all three to enter every war together. Article V also declared that the pact did not affect the existing political relations between each contracting party and the Soviet Union. Its provisions combined deterrence of the United States with a reservation concerning Soviet relations, reflecting diplomatic calculations at the time of conclusion. Germany's later war with the Soviet Union does not, by itself, justify interpreting the 1940 alliance as an agreement from the outset to attack the Soviet Union jointly.

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Article IV required the three governments to appoint representatives and convene joint technical commissions as soon as possible to address implementation. Notes exchanged between Japan and Germany on the same day added important qualifications: commission decisions could take effect only with the approval of the governments concerned, and whether a contracting party had been attacked within the meaning of Article III would also be determined through consultation among the three powers. These were procedures for cooperation, not a supranational body empowered to decide independently on war for its member states.

In his answers to the Privy Council, Matsuoka explained that once consultations established that an attack had occurred, the countries were to fight together, but each would determine and discuss the timing and manner of its assistance. The text, its interpretation, and subsequent actions therefore require separate consideration. Similarly, Germany's commitments in the exchanged notes to provide industrial and technical resources and help obtain raw materials cannot be treated as records of aircraft or fuel already delivered to Japan simply because those promises appeared in writing.

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Privy Council members asked about more than the alliance's prestige. On September 26, Councillor Kawai pressed for an explanation of how long material supplies would last in a prolonged war against the United States. Planning Board President Hoshino replied that oil supplies were especially dependent on the United States, with reliance on imported aviation gasoline particularly pronounced. A long war could not be sustained solely by resources within Japan, Manchuria, and China. He proposed securing oil sources in the Netherlands East Indies and elsewhere.

Councillor Ishii also observed that the pact did not prohibit a separate peace. Matsuoka replied that he regarded preventing war as its purpose and had not taken the initiative to request such a clause during negotiations; an agreement could be made later if war broke out. These discussions show that the alliance had not resolved questions of resource supply or how a war would be ended. Government declarations of preparedness should likewise not be equated with the actual capacity to sustain a prolonged war.

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Subsequent actions revealed strategic differences. Japan concluded a neutrality pact with the Soviet Union in April 1941, whereas Germany attacked the Soviet Union on June 22 without formally notifying Japan beforehand. Debate within the Japanese government over northern and southern expansion continued. The Tripartite Pact did not automatically lead Japan to adopt a Soviet policy identical to Germany's. The aspiration to cooperate did not eliminate differences rooted in national decision-making and battlefield interests.

On December 11, 1941, Japan, Germany, and Italy signed a separate joint-action agreement in Berlin. The new document expressly prohibited any of them from concluding an armistice or peace with the United States or Britain without complete mutual agreement. The signatories were Hiroshi Ōshima for Japan, Alfieri for Italy, and once again Ribbentrop for Germany. This was an additional constraint introduced in the circumstances of war, not a provision already present in the six-article pact of 1940. The history of implementing the Tripartite Pact therefore also encompasses subsequent negotiations, separate agreements, and continually changing strategic choices.

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