What ruling principle allowed the Holy Roman Empire to allow individual rulers to choose their religion after the Thirty Years' War?

The principle of Religious Autonomy allowed individual rulers within the Holy Roman Empire to select the religion of their own territories after the Thirty Years' War. This was established formally in the Peace of Westphalia in 1648, which ended the conflict and recognized the rights of various states and rulers to determine their own religious affiliations. This shift marked a significant change in the way religious authority and political governance were viewed, allowing for a degree of independence from the overarching control of the Catholic Church and the Holy Roman Emperor.

The Peace of Westphalia sought to bring stability to a region that had been devastated by religious conflict, and by recognizing the right of rulers to choose their own faith, it facilitated a more localized approach to governance. This helped to reduce religious strife by acknowledging the diverse beliefs present within the empire and legalizing the existence of Protestantism alongside Catholicism.

In contrast, feudalism refers to a social and economic system based on land ownership and obligations, while secularism promotes the separation of religion from political affairs. Divine Right holds that monarchs derive their authority directly from God, which does not accommodate the choice of religion by individual rulers. Thus, Religious Autonomy is the most accurate principle governing the situation following the Thirty Years' War.