 He befriended numerous fellow members of the Polish diaspora and became involved in a local underground group of the "Polska Organizacja Wojskowa" (Polish Military Organization, abbreviated ""POW"" in Polish).After the Russian Revolution, Okuniewo was seized by Bolshevik Russia, and Mostowicz's family moved back to newly reborn Poland, where they bought a small village.Also in 1918, Tadeusz moved to Warsaw, where he joined the Polish Army.