Why might the action of the Seljuks in conquering Southwest Asia have ignited the Christian Crusades?
The conquering of Jerusalem and the threatening of Constantinople brought the Western Christians nations to aide of the Eastern Roman Empire.
The king of the Eastern Roman Empire appealed to the Pope the leader of the Western Roman Catholic Church for help in fighting the Seljuk Turks.
In his appeal the leader of Eastern Roman Empire made allegations that the Seljuk Turks were abusing Christian pilgrims to the Holy Sites in Jerusalem and were enslaving Christians in the cities and areas that they conquered.
The Pope responded to the appeal by calling for a Holy Crusade to reconquer Jerusalem and freeing the Christian people from Islamic slavery.
Many nobles in Europe needing land answered the call hoping to establish new kingdoms for themselves in the mideast and southwest Asia.
The allegations though possibly exaggerated had elements of truth.
The previous Muslim rulers of Jerusalem had allowed Christian pilgrims free access to the Christian Holy Sites in Jerusalem.
The Seljuk Turks recent converts to Islam wanted Jerusalem to be a Holy City similar to Mecca. Non Muslims are not allowed to enter Mecca under pentalty of death. The Seljuk Turks felt that imprisoning and enslaving Christian pilgrims was a kinder act that killing them.
Also the Turkish army did enslave Christians and forced them to serve in the army. The Seljuk Turks felt that the religion of Islam gave them permission to enslave non muslims.
The allegations of the mistreatment of Christians in Jerusalem and other parts of the Eastern Roman Christian Empire enflamed Western Europe and lead to the Crusades.