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who said shoot them all and let god sort them out
Prior to the massacre of Béziers, it was reported that Arnaud Amalric, when asked how to distinguish Cathars from Catholics, responded, Kill them all! God will know his own.“
who was anraud amalric
Arnaud Amalric was a Roman Catholic Cistercian abbot who played a prominent role in the Albigensian Crusade.

Question: what was the crusade
Self-contained rewrite: what was the albigemsian crusade