The First Crusade began when the Seljuk Turks invaded Jerusalem and Christians could no longer travel to the Holy Land.
The Byzantine Empire was worried the the Turks would invade them, so Pope Urban II readied a speech to get ready for a Crusade.
Jerusalem has been taken by the Turks.
...you shall be given eternal life automatically.
Pope Urban II told the people of western Europe that any man who shall become a crusader will be given eternal life automatically.
Soon 60,000 people became soldiers and the Pope was ready and happy. Godfrey of Bullion and Pope Urban II led the soldiers to Jerusalem.
There is too many of them!
When the Christians reached Jerusalem they took over the city in a bloody battle this would be the most successful crusade.
There would be 9 other crusades. The first Crusade would be the most successful. In the next crusade the Christians would lose the city and never fully retake it. Therefore 7 other bloody crusades would happen.