How was the fourth crusade different from others?

The fourth crusade was very different from the three before it. And all because it ended with some paradox. Everyone knows that the pretext for the crusades was the return of the Holy Sepulcher and the struggle for the holy land. The fourth crusade was initiated by the Pope and ended with the fact that the crusaders not only won, but also completely plundered Constantinople, at that time the center of the peasant faith, and this is the paradox.