Complex sentence: During the Holocaust, the Jewish population of the town was first concentrated in a small ghetto, in 1942 moved to the Warsaw Ghetto, and afterwards to the Treblinka extermination camp.
Split into simpler sentences: During the Holocaust, the Jewish population of the town was first concentrated in a small ghetto. In 1942, the town moved to the Warsaw Ghetto and was later moved into the Treblinka extermination camp.