The Pope calling on crusades to invade the Holy Land and retake the land from Muslims
Before the Crusades reached the Holy Land Turkish troops had killed most of the untrained and poorly equipped peasants.
The nobles and knights found Muslims unorganized and not prepared in Jerusalem. After fighting for a while the Europeans took Jerusalem they made 4 kingdoms
The kingdoms the Europeans developed didn't last and the Muslims started taking back what was theirs. The Europeans launched more crusades but they lost due to poor planning.
The third Crusade happened after the Muslims retook Jerusalem. The German and French kings helped the Europeans. The German king died and the French king left and king Richard was left to face his opponent Saladin and his army.
Yayy! We won the final war!
Other crusades followed but none were successful. The Muslims had taken back Holy Land in 1291.