The Fourth Crusade lasted from 1202-1204. Instead of attacking Jerusalem, the crusaders attacked Constantinople. They stole statues, money, paintings and jewelry. They burned libraries. They destroyed churches. Their ridiculous excuse was that they needed money to defend Constantinople from the same fate as Jerusalem, as well as to fund the rescue of Jerusalem. The people of Constantinople did not find this excuse acceptable, and they were filled with hatred for the west.
The problem crusades
Around 1095, a new group of Arabs took control of Jerusalem. They closed the city to Jewish and Christian pilgrims.
The Pope acted. He called for a crusade - a volunteer army whose goal was to retake Jerusalem. Many people volunteered. About 30,000 men left Western Europe to fight in Jerusalem.
Crusade the thing the use
Each crusader had a huge red cross, made out of fabric, stitched onto their shirts or armor. It made all crusaders, irrespective of rank or background, appear to be a unified army. It reminded the crusaders that they were fighting a holy cause. The red cross was added to flags and banners