Religion and spirituality have guided human thoughts, values, and behaviors for centuries. For the samurai of Japan and the knights of Europe, various doctrines of religious and spiritual thought provided the foundations for their unofficial warrior codes. The ethical and moral implications from these ideologies also provided justification, in some cases, for acts of military violence.
It is important to note that religion played different roles in each society - where Europe had a highly centralized church and state, Japan was quite different and lacked an equivalent centralized authoritative religious system. Overall, religion/spirituality provided both the samurai and the knight with certain fundamentals to guide their thoughts and actions.