Japan's declaration complicates Axis access to supplies and the French fleet

Japan's entry would cut Germany off from Japanese material supplies and promise further British reinforcements in the Mediterranean. An Axis attempt to compensate by seizing the French fleet could break the armistice almost immediately. That could undermine the Vichy government, renew French resistance, or allow warships to escape and join Britain. Fewer ships were concentrated at Toulon than when Germany historically attempted a seizure, and Italy could not make the drive alone. The likelier outcome in this scenario is that Hitler leaves the agreement intact while expecting Britain to make peace. Japanese ships could not arrive before Mers-el-Kébir, so that confrontation is expected to proceed much as it did historically. Hitler would probably continue trying to force Britain out through air attack before the new ally could change the military balance.