You probably mean the Crusades.
Jerusalem has some significance for Christians as that is where Jesus was crucified but really it is just a city there is nothing holy or important about Jerusalem for Christians. There is nothing important about going there.
The Muslim Empires Conquered Jerusalem which was considered Holy to the Christians also.
It is the Resurrection Church or Catedral and other sites.
If they want to. I don't believe that it is mandatory.
Jerusalem. This is the same place Jews and Muslims go as all 3 religions see this city as their "Holy City"
Ask them. Go to one of each religion and ask.
Because of all the riches and power it held:money,power,revenge and obviously religon.
For Christians, Jerusalem represents a place of "reverence" due to the fact that it was the place where (i) Jesus Christ was born and (ii) where the Christian faith was born. Note: Although Christian tradition states that Jesus was born in Bethlehem, it is only 10 kilometers (6 miles) from Jerusalem.
the thing that makes it go is the gas
The First Crusade was initiated in 1095 to restore Christian access to holy sites in and around Jerusalem.
Because Catholics are Christians and Christ was a Jew. Christians believe he is the Jewish messiah. Christ died and was resurrected in the city. It is therefore a holy Christian site, worthy of pilgrimage.
Jerusalem is a pilgrimage site because it is "The City of God" for both the Christians and Jews. It is the original site for Solomon's Tabernacle. It is also the location of the crucifixion of Christ and his resurrection. Millions worldwide who are believers or Christian/Jewish people dream of being able to go to Jerusalem and to go to the wailing wall, which is part of the foundation of the tabernacle. Jews will get the tabernacle or rather temple rebuilt in the future. This is a goal of both Jews and Christians. And it will be located in Jerusalem.