When Sara requests that Hogan take her to a Mexican camp, he agrees because he had previously arranged to help the Mexican revolutionaries attack the French garrison in exchange for a portion of the garrison's strongbox if they are successful.
Because he had previously arranged to help the Mexican revolutionaries attack the French garrison in exchange for a portion of the garrison's strongbox if they are successful. This is what he agrees. Hogan take her to a Mexican camp. Sara requests this.