2. The rise of the Ottoman Turks. The Ottoman Turks were a Muslim people who had been expanding their territory in Anatolia (modern-day Turkey) for several centuries. The Byzantine Empire had been able to contain the Ottomans, but after the Fourth Crusade, the Ottomans were able to conquer much of Anatolia and eventually the Balkans. The Ottoman Empire became a major power in the world and a major threat to Christendom.
3. The loss of Christian holy sites. The Fourth Crusade resulted in the loss of many Christian holy sites in the Holy Land, including the Church of the Holy Sepulchre in Jerusalem. This was a major blow to the morale of Christians and made it more difficult for them to travel on pilgrimage to the Holy Land.
4. The disunity of the Christian world. The Fourth Crusade also contributed to the disunity of the Christian world. The crusaders were from a variety of countries and had different goals and motivations. This led to conflict and division, which made it difficult to mount effective crusades in the future.
5. The rise of anti-Semitism. The Fourth Crusade also led to a rise in anti-Semitism. The Jews of Constantinople were blamed for the city's fall to the crusaders, and they were subjected to violence and persecution. This anti-Semitism spread to other parts of Europe and helped to pave the way for the Holocaust.