Why balance-of-power logic made a solo Pacific war unlikely

A purely Anglo-Japanese war was unlikely because the United States could not comfortably let Britain defeat Japan alone and emerge as the dominant outside power in Asia. The same logic applied to Britain and France in Europe: neither could safely leave the other to fight Germany or Italy alone. A solo victory could let the winner reshape the regional order, while a solo defeat would endanger the bystander. Cooperation therefore followed from competitive balance-of-power interests as much as friendship. Japanese war planning had to anticipate combined opponents rather than isolate each naval power in turn.