The 2nd Crusade was launched in 1147 to stop the Muslims from taking more land. Though it failed because of poor planning and heavy losses.
The 3rd Crusade began after the Muslims retook Jerusalem in 1189. The main opponent was Saladin, leader of the Muslims. Richard and Saladin negotiated and fought. In the end they came home with Jerusalem still in Muslim hands.
This is my land!
The 4th Crusade, in 1201, French knights arrived in Venice to sail to the Holy Land. There wasn't money to pay for the voyage. The knights conquered Zara for payment. They attacked Constantinople and acquired many treasures.
I don't trust you anymore!
Crusaders learned about products like apricots, rice and cotton cloth.
Kings gained power because many knights and nobles died in the crusades. The kings seized lands without owners and gained influence at the Pope's expense.
Christians, Jews, and Muslims had lots of problems beginning with Jews distrusting Christians. And Muslims and Christians began to distrust each other.