Final answer:
John Calvin was invited to lead the Protestant Reformation in the city-state of Geneva, Switzerland and imposed a strict moral code working in conjunction with its secular rulers.
Step-by-step explanation:
The city-state being referred to in the question is Geneva. John Calvin, a religious leader, was invited to lead the Protestant Reformation in Geneva and imposed a strict moral code working in conjunction with its secular rulers. Geneva became the most important center for the teaching and spreading of Protestantism.