Answer:
-To be forgiven for past sins. The Pope offered forgiveness for anyone who took part. This was important for knights who had killed many people in battle.
-To see the world, have an adventure and prove their bravery.
-To get land overseas. This was tempting for a younger son who would not inherit his father's lands.
Serfs, peasants who belonged to their lord, joined the Crusades because the -Pope promised them their freedom if they went.
-To gain wealth.
-Kings encouraged troublesome knights to go on Crusade because it got them out of the country.