A secular state is one in which religion is expressly forbidden from playing a direct role in government. In some cases, a secular state may move beyond the prohibition of active religious involvement in politics and pursue policies deliberately designed to reduce the role of religion in civil or national life. Some extreme forms of secular state may replace religion with a secular cult of the state or the leader. In other cases, however, a secular state may be designed not to limit or attack religious practice but to allow for the free exercise of different forms of religion within a single state.
The idea of a secular state, although owing something to the decidedly non-spiritual rituals used to honor Roman emperors as an expression of patriotism, is mostly a product of the Enlightenment. The thinkers of the Enlightenment, although often religious, were troubled by the role that organized religion had played throughout human history. Consequently, these thinkers, particularly the French philosophes, were skeptical of organized religion and generally argued that religion should be excluded from political life.
The two most important revolutions of the 18th century, the American Revolution and the French Revolution, were both inspired in part by the anti-religious ideas of the Enlightenment, but produced very different outcomes. The framers of the American Constitution, while mostly men of faith, crafted a document that most scholars believe was intended to keep any one religion from dominating the government. It does so by preventing the government from establishing a state religion. This variety of secular state is now quite common in the western world, where religion is generally tolerated, but the machinery of government is kept free from the official control of a single sect.
The French Revolution initially produced a state similar to that created in America but, during its most radical period, went on to promote a cult of the citizen. This cult attempted to replace conventional religious belief with faith in the state and nation. Such a policy proved unpopular and this experiment disappeared with the end of the radical phase of the French Revolution.
Communist nations are typically avowedly opposed to religious belief. The largest secular state in the modern world is the People's Republic of China, which tolerates some religious practice but prefers a non-religious worldview. Other communist states have acted more aggressively against religion. The Soviet Union, especially under Joseph Stalin, was militantly secular. Efforts to spread atheism were ultimately unsuccessful and were abandoned during the darkest days of the Second World War in favor of a tactical, emergency alliance with the Orthodox Church. Much violence, however, was perpetrated during the campaign to stamp out religion.
Modern Turkey is another major example of a secular state. The founders of the modern Turkish state held that religion had caused stagnation in the Ottoman Empire and pursued policies to exclude religion from public political life and exclude religious views from government. The secular nature of government in Turkey has begun to erode in recent years as political parties with religious roots have gained high elected office. In 2011, this is part of a larger trend in the Islamic world where the first wave of anti-colonial governments tended to be strongly secular but where more recent governments have had stronger ties to religion.