Complex sentence: Kressel's parents and sister died in The Holocaust during World War II, after which Kressel emigrated to the United States and entered Chaim Berlin High School in 1947, from which he graduated in 1951.
Split into simpler sentences: Kressel's parents and sister died in The Holocaust during World War II, after which Kressel emigrated to the United States. He entered Chaim Berlin High School in 1947 and graduated in 1951.