Japan's entry made it possible to destroy the East Asia Squadron without drawing a large Royal Navy force away from Europe. The German naval showpiece contained experienced crews and capable officers, so its isolation endangered more than a collection of hulls. HMAS Australia also overmatched the German armoured cruisers to the south. Von Spee's eastward movement offered an escape from these converging allied forces, even though it did not resolve his shortage of secure bases.
Chapter · 44:16-48:20
The Anglo-Japanese alliance trapped von Spee
Once Japan entered the war, von Spee faced destruction by the Japanese fleet to the north or HMAS Australia to the south and chose to cross the Pacific.