Fastsnake wrote:What other useful thing can the japanese army can do otherwise?
Go for ABDA possessions in Asia, as in WWII? The French had Indochina; The British Singapore, Oz and Hong-Kong; the Dutch the East Indies. Targets weren't lacking, and as in WWII the Japanese still badly needed the coal, fuel, and food.
That's a good question for alternate historians, though: Were Japan simply in position to be helpful for the Central Powers, aside from tieing much needed units from their colonies in Asia?
Japan joining the CP would be the War in the Pacific, without the US spoiling the fun... for a while. However, as Japan I'd see grabbing Port Arthur and Vladivostock as a primary objectives, just like in 1905, this time with the aim of keeping it (and Manchuria) for good, and prevent the use of these ports as leverage against Japan.
Remember, the Japanese got mauled at Port Arthur in 1904-1905, but the Russians fared even worse and they lost. So the Japanese knew very well the state of Russian troops in Siberia : massive army, yes, but badly led, slow, and with huge logistical issues.