Complex sentence: In 1919 his father refused to take an oath of allegiance to Czechoslovakia, the family was then expelled from Bratislava and moved to Budapest, where he entered the Péter Pázmány University.
Split into simpler sentences: In 1919 his father refused to take an oath of allegiance to Czechoslovakia, whereby his family was expelled from Bratislava. They moved to Budapest, where he entered the Péter Pázmány University.