What is 4 reasons why people joined the crusades?

1) Adventure: Most people wanted to go explore, and crusades was one way of a group of people going to a "somewhere"(israel) to fight a war.
2) Treasure: The church and people of authority wanted to gain riches, and crusades was a way.
3) Heaven: The church decreed that anybody that joined the crusades and fought their enemies would have a free passage to heaven. They were 'fighting' for God anyhow.
4) Fear: Many people feared that if Islam took over Jerusalem, where Christianity started, the Christian faith would die in Europe too, and then everybody would become Muslim

hope this helps