Final answer:
The pope excommunicated all Crusaders taking part in the 4th Crusade because they attacked Constantinople and sacked the city.
Step-by-step explanation:
The pope excommunicated all Crusaders taking part in the 4th Crusade because they attacked Constantinople and sacked the city. The Fourth Crusade was initially intended to focus on expelling Muslim rulers from Christian lands, but it deviated from its objective and turned against the Byzantine Empire. The crusaders became involved in the internal politics of Byzantium and attacked Constantinople, causing significant damage to the crusading movement and straining relations between the Greek Orthodox and Catholic churches.
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