Complex sentence: Znaniecki came to Chicago in the United States in 1914 and returned to the Second Polish Republic in 1920 to accept the first Polish chair in sociology at the University in Poznań.
Split into simpler sentences: Znaniecki came to Chicago in the United States in 1914 and returned to the Second Polish Republic in 1920. There he became the first Polish chair in sociology at the University in Poznań.