Final answer:
The 1555 Peace of Augsburg implemented the principle of 'cuius regio, eius religio,' giving rulers the right to determine the religion of their own territories within the Holy Roman Empire. Hence, the correct answer is option A.
Step-by-step explanation:
The 1555 Peace of Augsburg concluded the early conflicts of the Lutheran Reformation within the Holy Roman Empire. The compromise enacted through this peace agreement was cuius regio, eius religio, which means 'whose realm, his religion.'
This principle allowed each ruler within the Holy Roman Empire to determine whether his state would embrace Lutheranism or Catholicism. It effectively ended the religious unity of the empire and set the stage for future religious and political conflicts, including the Thirty Years' War, which would further shape the religious landscape of Europe.