Which event marked a significant point of contention between Martin Luther and the Holy Roman Emperor?

The Diet of Worms in 1521 was a crucial event that underscored the conflict between Martin Luther and the Holy Roman Emperor, Charles V. At this assembly, Luther was summoned to defend his teachings and writings, which challenged the Catholic Church's practices and authority.

During this gathering, Luther famously refused to recant his statements, asserting that his conscience was bound to the Word of God. This bold stance was significant because it showcased not only Luther's commitment to his beliefs but also his defiance against the emperor's authority and the Catholic Church. The outcome of the Diet resulted in a papal bull that condemned Luther's ideas, declaring him an outlaw. This event catalyzed the Protestant Reformation, resulting in a profound shift in religious and political dynamics in Europe.

The other options, while historically relevant, do not directly pertain to the specific clash between Luther and the Holy Roman Emperor. The Act of Supremacy dealt with England's break from the Catholic Church, the Great Schism refers to the division within the Catholic Church itself, and the Spanish Inquisition primarily focused on enforcing Catholic orthodoxy in Spain. Thus, the Diet of Worms distinctly represents the pivotal moment of confrontation between Luther and the Holy Roman Empire.