Protestants generally trace their separation from the Roman Catholic Church to the 1500's, which is sometimes called the magisterial Reformation because it initially proposed numerous radical revisions of the doctrinal standards of the Roman Catholic Church (called the magisterium). The protest erupted suddenly, in many places at once but particularly in Germany, during a time of threatened Mohammedan invasion¹ which distracted German princes in particular. To some degree, the protest can be explained by the events of the previous two centuries in Western Europe.
Unrest in the Western Church and Empire, which culminated in the Avignon Papacy (1308 - 1378), and then the papal schism (1378-1416), excited wars between princes, uprisings among the peasants, and widespread concern over corruption in the monastic system. In addition, the humanistic Renaissance was stimulating an unprecedented academic ferment, with a concomitant concern for academic freedom. Earnest theoretical debates were ongoing in the universities concerning the nature of the church, and the proper source and extent of the authority of the papacy, of councils, and of princes. One of the most disruptive and radical of the new perspectives came first from John Wyclif at Oxford and then from Jan Hus at the University of Prague. Within the Roman Catholic Church, this debate was officially concluded by the Council of Constance (1414-1418), which executed Jan Hus, and posthumously burned Wyclif as a heretic. However, while Constance confirmed and strengthened the Medieval conception of church and empire, it could not entirely resolve the national tensions, nor the theological tensions which had been stirred up during the previous century. Among other things, the council could not prevent schism and the Hussite Wars in Bohemia.
To some extent, the protest that began when Martin Luther, an Augustinian monk and professor at the University of Wittenberg, called for reopening of debate on the sale of indulgences (or as tradition holds, literally nailed his 95 theses to the door of the Wittenberg Church). It was a sudden outbreak with new and irresistible force of discontent which had been pushed underground but not resolved.
Parallel to events in Germany, a movement began in Switzerland under the leadership of Huldreich Zwingli. These two movements quickly agreed on most issues, as the recently introduced printing press spread ideas rapidly from place to place but some unsolved differences kept them separate. Some followers of Zwingli believed that the Reformation was too conservative, and moved independently toward more radical positions, some of which survive among modern day Anabaptists. Other Protestant movements grew up along lines of mysticism or humanism (cf. Erasmus), sometimes breaking from Rome or from the Protestants, or forming outside of the churches.
After this first stage of the Reformation, following the excommunication of Luther and condemnation of the Reformation by the Pope, the work and writings of John Calvin were influential in establishing a loose consensus among various groups in Switzerland, Scotland, Hungary, Germany and elsewhere. The separation of the Church of England from Rome under Henry VIII, beginning in 1529 and completed in 1536, brought England alongside the Reformation. However, change in England proceeded more conservatively than elsewhere in Europe and alternated between traditional and Protestant sympathies for centuries, progressively forging a stable compromise. Thus, the West was permanently divided into Catholic and Protestant.