Back when China was under the nationalist government (1911 to 1939) and during the late Qing Dynasty (1939 to 1911), we were indeed very weak. That all changed under Mao Zedong and the CCP, and we began our campaign of revenge in 1949. This campaign is not quite finished. We still must take back South China Sea, East China Sea and Southern Tibet.
mongolia and siberia is much better but harder,I think.