A cikin Yaƙin Sino-Japan na Farko, an nada Ōyama babban kwamandan rundunar sojojin Japan ta biyu, wanda bayan ya sauka a tsibirin Liaotung, ya ɗauki
Port Arthur ta hanyar hadari, kuma daga baya ya tsallaka zuwa Shantung, inda ya kama sansanin Weihaiwei. Bayan yaƙin, ɗan jaridar Amurka Trumbull White ya raina Ōyama saboda rashin iya kame sojojinsa a lokacin Kisan gillar Port Arthur.