The following chapter examines the evolution of the U.S–Japan relations from the 1930 London Naval Agreement to Japan’s 1936 alliance with Nazi Germany under the Anti-Comintern Pact. It argues that U.S. efforts to enforce naval disarmament and maintain neutrality gradually eroded in response to Japan’s militaristic expansion, beginning with the Manchurian Incident. U.S. economic support for China and rising concerns over Japanese ambitions in the Dutch East Indies indicated evolving American priorities in East Asia. Despite initial attempts to remain impartial through legislation such as the Neutrality Acts, the U.S. transitioned toward active support for its allies via the 1939 cash- and- carry policy and the 1941 Lend Lease Act. Ultimately, the chapter contends that these measures, while intended to deter aggression, failed to restrain Japan and instead accelerated the path toward war in the Pacific.