Leviathan was a book born of necessity. For more than a century and a half — from the German Peasants’ War in 1524 to the English Civil War in the mid-17th century — Catholics and Protestants had slaughtered each other in the name of the one true God. The Thirty Years War alone, between 1618 and 1648, devastated Europe to a degree not seen again until the wars of the 20th century.
Only in 1648, with the signing of the series of treaties known as the Peace of Westphalia, were Europeans able to bring their religious wars an end. The treaties not only established the principle of non-interference in the domestic affairs of sovereign states, but they also laid the groundwork for the separation of religion and politics, a concept that over time became a fundamental principle for liberal democratic order.