Crusaders participated in the Crusades for a number of reasons beyond just reclaiming the Holy Land for Christianity. Some of those reasons included forgiveness of sins, travel opportunities, the desire of younger nobles to obtain land in the Middle East, establishment of new cultural contacts between the East and West and the establishment of new trade routes and commercial opportunities.
The First Amendment to the U.S. Constitution says that everyone in the United States has the right to practice his or her own religion, or no religion at all.
