Were the Crusades caused primarily by religious devotion or by the desire for political and economic gain?
The Crusades were called because of religious devotion but the call was answered because to the desire for political and economic gain.
The Pope called for the Crusades because the Seljuk Turks who had recently conquered Jerusalem from the Fatima Shite Muslims changed the conditions for Christian pilgrims.
Under the Fatima Muslims Christians were allowed to freely visit the "Christian Holy Sites" in Jerusalem. The Seljuk Turks wanted Jerusalem to be a Holy City for Muslim like Mecca. This meant that only Muslims could be allowed to visit the city. Reports of Christian pilgrims being killed or taken into slavery by the Turks infuriated the Christians in Western Europe. This was religious devotion.
A call went out for soldiers to take Jerusalem from the Seljuk Turks.
Many second and third sons answered the call. In the Holy Land they could carve out principalities and become Lords. In Western Europe the land was all taken. The call was answer by most Crusaders for dreams of political and economic gain.
The Eastern Roman Empire had appealed for help became of the amount of land and control that they had lost to the Seljuk Turks.
The agreement with the Pope was that the Crusaders would liberate not only Jerusalem but the lands lost to the control of the Turks.
When the Crusaders liberated the land they kept the land for themselves. This showed that the reasons that the Crusaders answered the call was not religious devotion but economic greed.
The call for the Crusades was made on the basis of religious devotion and justice. The call was answered on the basis of political and economic gain.