Complex sentence: While serving as Apostolic Nuncio to Bavaria, Eugenio Pacelli (later Pius XII) was in Munich during the Spartacist Uprising of 1919, which saw Communists burst into his residence brandishing guns--an experience which contributed to Pacelli's lifelong distrust of Communism.
Split into simpler sentences: While serving as Apostolic Nuncio to Bavaria, Eugenio Pacelli (later Pius XII) was in Munich during the Spartacist Uprising of 1919, which saw Communists burst into his residence brandishing guns. An experience which contributed to Pacelli's lifelong distrust of Communism.