France and the Netherlands would probably support Britain, with the United States likely to join either immediately or after the blockade demonstrates its effectiveness. Germany and Italy are not yet treaty-bound to Japan, so prestige, colonial rewards, and the chance to recover Tsingtao could even tempt them to contribute ships on the Allied side. The Soviet Union has its own active frontier conflict and sphere-of-influence disputes with Japan, giving Moscow a separate reason to participate. The resulting mobilization would strengthen Allied naval readiness and could postpone, reshape, or complicate a later European war.
Chapter · 2:12:28-2:18:40
A Pacific war scrambles the alliance map
Because the Tripartite Pact does not yet exist, war with Japan could assemble an unusually broad maritime coalition and delay or redirect the European conflict.