Final answer:
The dominant motive for joining the First Crusade was religious.
Step-by-step explanation:
The dominant motive for joining the First Crusade was religious. The Crusades were a series of military campaigns sanctioned and endorsed by the Catholic Church with the aim of retaking the Holy Land from Muslim control. People from all walks of life, including knights, peasants, and clergy, were inspired by religious fervor and the promise of spiritual rewards to join the Crusade. The belief in the religious significance of the mission, as well as the desire to protect and defend Christianity, were key driving factors behind individuals' decision to participate.
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