Germany and Italy would face a more concentrated opposing fleet if Japan joined Britain. Britain could reduce its Far Eastern requirements and deploy more ships to the Mediterranean and Home Fleet. For Italy, reaching Alexandria or blocking Suez would offer a way to obstruct Japanese reinforcements arriving through the Indian Ocean. Japanese ships could still enter through Gibraltar, but that route would be harder to sustain. A secure Indian Ocean would also let Britain relocate ships and mobile support facilities closer to the Mediterranean. The timing limits the Axis response: German U-boat strength has yet to reach its later peak, the Greco-Italian War historically begins in October 1940, and the Afrika Korps deploys in February 1941.
Chapter · 50:55-57:23
Suez becomes the Axis pressure point
Japan's entry makes the Mediterranean and Suez central because the Indian Ocean becomes a safer Allied support area.