The Renaissance and Reformation eras witnessed a resurgence in religious fervor, as evidenced by the proliferation of new religious orders, confraternities, and popular devotions in the Catholic world, and the appearance of increasingly austere Protestant sects such as the Calvinists. This era of interconfessional rivalry permitted an even wider scope of theological and philosophical speculation, much of which would later be used to advance a religiously skeptical world-view.

Criticism of Christianity became increasingly frequent in the 17th and 18th centuries, especially in France and England, where there appears to have been a religious malaise, according to contemporary sources. Some Protestant thinkers, such as Thomas Hobbes, espoused a materialist philosophy and skepticism toward supernatural occurrences. In the late 17th century, Deism came to be openly espoused by intellectuals such as John Toland, and practically all the philosophes of 18th-century France and England held to some form of Deism. Despite their ridicule of Christianity, many Deists held atheism in scorn. The first openly atheistic thinkers, such as Baron d’Holbach, appeared in the late 18th century, when expressing disbelief in God became a less dangerous position. David Hume was the most systematic exponent of Enlightenment thought, developing a skeptical epistemology grounded in empiricism, undermining the metaphysical basis of natural theology.

The French Revolution took atheism outside the salons and into the public sphere. Attempts to enforce the Civil Constitution of the Clergy led to anti-clerical violence and the expulsion of many clergy from France. The chaotic political events in revolutionary Paris eventually enabled the more radical Jacobins to seize power in 1793, ushering in the Reign of Terror. At its climax, the more militant atheists attempted to forcibly de-Christianize France, replacing religion with a Cult of Reason. These persecutions ended with the Thermidorian Reaction, but some of the secularizing measures of this period remained a permanent legacy of French politics.

The Napoleonic era institutionalized the secularization of French society, and exported the revolution to northern Italy, in the hopes of creating pliable republics. In the nineteenth century, many atheists and other anti-religious thinkers devoted their efforts to political and social revolution, facilitating the upheavals of 1848, the Risorgimento in Italy, and the growth of an international socialist movement.

In the latter half of the 19th century, atheism rose to prominence under the influence of rationalistic and freethinking philosophers. Many prominent German philosophers of this era denied the existence of deities and were critical of religion, including Ludwig Feuerbach, Arthur Schopenhauer, Karl Marx, and Friedrich Nietzsche.

(Source: Wikipedia)

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