While the first three Crusades were launched in an effort to reclaim Jerusalem from Muslims, the Fourth Crusade, begun in 1202, pitted Christians against Christians: Roman Catholics against Orthodox.
Real Crusades History on MSN

The crusade that betrayed Christianity

Instead of reaching Jerusalem, the Fourth Crusade diverted to Constantinople, culminating in the sack of the Byzantine capital in 1204. This episode examines how political ambition and financial ...