A ranar 16 ga Agusta, 1920, a lokacin yakin Warsaw, an sanya shi a matsayin kwamandan jami'in sojan doki na 4 na Poland, wanda daga baya ya zama ainihin abin da ake kira "Nieniewski's Operational Group" a lokacin yakin Warsaw.
Yaƙin Kogin Niemen. Bayan ƙarshen tashin hankali na Yakin Poland-Soviet, Nieniewski ya kammala karatun Janar Janar kuma a ranar 10 ga Janairu, 1921, an ba shi mukamin Kanar Sojan doki.