Complex sentence: Pius XII was Pope from 2 March 1939 to 9 October 1958, a period that straddled the Second World War period, which saw the destruction of European Jewry in the Holocaust, and saw the establishment of the State of Israel in 1948.
Split into simpler sentences: Pius XII was Pope from 2 March 1939 to 9 October 1958. His papacy covered the Second World War period, which saw the destruction of European Jewry in the Holocaust, and saw the establishment of the State of Israel in 1948.