Europe experienced a period of dreadful calamities from the early 14th century. These culminated in a devastating pandemic known as the Black Death, which killed about one-third of Europe's population. Around 1500, the population of Europe was about 60–85 million people—no more than 75 percent of the mid-14th-century demographic maximum. Due to a shortage of workforce, the landlords began to restrict the rights of their tenants which led to rural revolts that often ended with a compromise.

The constant fear of unexpected death was mirrored by popular artistic motifs, such as the allegory of danse macabre ('dance of death'). The fear also contributed to the growing popularity of Masses for the dead. Already detectable among early Christians, these ceremonies indicated a widespread belief in purgatory—a transitory state for souls that needed purification before entering heaven. Fear of malevolent magical practice was also growing, and witch hunts intensified.

At the end of the 15th century, the sexually transmitted infection known as syphilis spread throughout Europe for the first time. Syphilis destroyed its victims' looks with ulcers and scabs before killing them. Along with the French invasion of Italy, the syphilis gave the background to the success of the charismatic preacher Girolamo Savonarola (d. 1498) who called for a moral renewal in Florence. He was arrested and executed for heresy, but his meditations remained a popular reading.
Historian John Bossy (as summarized by Eamon Duffy) emphasized that "medieval Christianity had been fundamentally concerned with the creation and maintenance of peace in a violent world. 'Christianity' in medieval Europe denoted neither an ideology nor an institution, but a community of believers whose religious ideal—constantly aspired to if seldom attained—was peace and mutual love."

The Catholic Church taught that entry into heaven required dying in a state of grace. Based on Christ's parable on the Last Judgement, the Church considered the performance of good works by the faithful, such as feeding the hungry and visiting the sick, as an important co-condition of salvation. Villagers and urban laypeople were frequently members of confraternities (such as the Archconfraternity of the Gonfalone), mutual-support guilds associated with a saint, or religious fraternities (such as the Third Order of Saint Francis). The faithful made pilgrimages to saints' shrines, but the proliferation in the saints' number undermined their reputation. There was a strong Biblical awareness, especially of the Gospels and Psalms.

Church buildings were richly decorated with paintings, sculptures, and stained glass windows. While Romanesque and

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The Reformation in Germanic countries was instigated by Martin Luther, however historians note that many of his ideas were pre-dated by Wycliff, Huss, Erasmus, Zwingli and others, both heretic and orthodox. Historian Peter Marshall has noted "In recent decades, scholars have become increasingly acclimatized to the idea that the Reformation was in important respects a continuation and intensification of trends within later medieval Catholicism, rather than simply a wholesale rejection of it."
Pope Leo X (r. 1513–1521) decided to complete the construction of the new St. Peter's Basilica in Rome. As the sale of certificates of indulgences had been a well-established method of papal fund raising, he announced new indulgences in the papal bull Sacrosanctis in 1515. On the advice of the banker Jakob Fugger (d. 1525), he appointed the pluralist prelate Albert of Brandenburg (d. 1545) to supervise the sale campaign in Germany. The Dominican friar Johann Tetzel (d. 1519), a leading figure in the campaign, applied unusually aggressive marketing methods. A slogan attributed to him famously claimed that "As soon as the coin into the box rings, a soul from purgatory to heaven springs". Frederick the Wise, Prince-elector of Saxony (r. 1486–1525) forbade the campaign because the Sacrosanctis suspended the sale of previous indulgences, depriving him of revenues that he had spent on his collection of relics.

The campaign's vulgarity shocked many serious-minded believers, among them Martin Luther, a theology professor at the University of Wittenberg in Saxony. Born into a middle-class family, Luther entered an Augustinian monastery after a heavy thunderstorm dreadfully reminded him the risk of sudden death and eternal damnation, but his anxiety about his sinfulness did not abate. His studies on the works of the Late Roman theologian Augustine of Hippo (d. 430) convinced him that those whom God chose as his elect received a gift of faith independently of their acts. He first denounced the idea of justification through human efforts in his Disputatio contra scholasticam theologiam ('Disputation against Scholastic Theology') in September 1517.

On 31 October 1517, Luther addressed a letter to Albert of Brandenburg, stating that the clerics preaching the St. Peter's indulgences were deceiving the faithful, and attached his Ninety-five Theses to it. He questioned the efficacy of indulgences for the dead, although also stated "If ... indulgences were preached according to the spirit and intention of the pope, all ... doubts would be readily resolved". Archbishop Albert ordered the theologians at the University of Mainz to examine the document. Tetzel, and the theologians Konrad Wimpina (d. 1531) and Johann Eck (d. 1543) were the …

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Andreas Karlstadt accelerated the implementation of Reformation in Wittenberg. On Christmas Day 1521, he administered the Eucharist in common garment; the next day he announced his engagement to a fifteen-year-old noble girl Anna von Mochau. He proclaimed that images were examples of "devilish deceit" which led to the mass destruction of religious art. Enthusiasts began swarming to Wittenberg. The Zwickau prophets, who had been incited by the radical preacher Thomas Müntzer (d. 1525), claimed that they had received revelations from God. They rejected transubstantiation and attacked infant baptism. Luther defended art as a proof of the beauty of the Creation, maintained that Christ's Body and Blood were physically present in the Eucharist, and regarded infant baptism as a sign of membership in the Christian community. To put an end to the anarchy, Frederick the Wise released Luther in March 1522. Luther achieved the Zwickau prophets' removal from Wittenberg, calling them fanatics. Karlstadt voluntarily left Wittenberg for Orlamünde where the local congregation elected him its minister. Luther visited most parishes in the region to prevent radical reforms, but he was often received by verbal or physical abuses. When he wanted to dismiss Karlstadt, the parishioners referred to his own words about the congregations' right to freely elect their ministers, and Karlstadt called him a "perverter of the Scriptures". Karlstadt was expelled from Electoral Saxony without a trial on Luther's initiative.

Luther condemned violence but some of his followers took up arms. Franz von Sickingen (d. 1523), an imperial knight from the Rhineland, formed an alliance with his peers against Richard von Greiffenklau, Archbishop-elector of Trier (r. 1511–1531), allegedly to lead the Archbishop's subjects "to evangelical, light laws and Christian freedom". Sickingen had demanded the restitution of monastic property to the grantors' descendants, stating that the secularisation of church property would also improve the poor peasants' situation. Sickingen and his associates attacked the archbishopric but failed at the siege of Trier. Sickingen was mortally wounded while defending his Nanstein Castle against the Archbishop's troops. Luther denounced Sickingen's violent acts. According to his "theory of two kingdoms", true Christians had to submit themselves to princely authority.
The Swiss Humanist priest Huldrych Zwingli would claim that he "began to preach the Gospel of Christ in 1516 long before anyone in our region had ever heard of Luther". He came to prominence when attended a meal of sausages in Zürich during Lent 1522, breaching the rules of fasting. He held disputations with the urban magistrates' authorization to discuss changes in church life, and always introduced them with the magistrates' support. In 1524, all images were removed from the churches…

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