Complex sentence: Influenced by Roman Dmowskis radical nationalist and social-Darwinist ideas National Democrats turned against other nationalities within the Polish lands, most notably Jews; anti-Semitism became one of key elements in NDs ideology.
Split into simpler sentences: Influenced by Roman Dmowskis radical nationalist and social-Darwinist ideas National Democrats turned against other nationalities within Polish lands, most notably Jews. Anti-Semitism became one of key elements in NDs ideology.