A revolution is a historical event or process that results in fundamental change in the way a society or political system is structured. Many different social and political changes can be called "revolutions," and there is no single correct way to categorize them. However, it is still important to have a general idea of what kinds of revolutions have occurred in history.

Revolutionary Wars

In history, the word revolution most often refers to the forceful expulsion of the government, either to change to a different governing system or to establish independence from another country. Sometimes, as with the American Revolution in the 1700s or the Russian Revolution of the 20th century, the overthrow of the government involves a long and bloody war. Another prominent example is the 1949 Communist Revolution in China, which succeeded only after Mao Zedong's Red Army defeated the Nationalists in a long-running civil war.

Government Overthrow

Sudden changes in government don't always happen through warfare. The French Revolution, one of the most important in Western history despite its ultimate failure, was characterized by violent riots and bloody crackdowns, but not large-scale war. And one of first popular uses of the word "revolution" for a change in government was in 1688, when England replaced Catholic King James II with Protestant William and Mary, an event known as the "Glorious Revolution" and remembered for its relative lack of violence. Other government overthrows are truly nonviolent, such as Czechoslovakia's 1989 "Velvet Revolution," which ended communism in the country through mass protests by the people.

Economic Revolutions

Revolutionary changes can also affect the economic systems in a society. The most famous example is the Industrial Revolution, which began in England in the late 1700s. As traditional methods of producing goods by hand and through direct human labor were replaced by factories and machines, the economies of England, Europe and later the whole world were radically transformed. Another example is the "Green Revolution" of the 20th century, when technological advances brought huge increases to the world's agricultural production, making food cheaper in the developed world but failing to end world hunger.

Social and Cultural Revolutions

Political revolutions can bring about major social changes, as the French Revolution did, but other transformations of society are separate from changes in governing structures. For example, the Protestant Reformation, when many of today's Christian denominations split from the Catholic Church, can be described as a revolution. A different kind of cultural transformation happened in the U.S. staring in the 1960s with the so-called "Sexual Revolution," which replaced strict traditional sexual morality with a modern culture where sex outside marriage, contraception and equal relationship roles for men and women are all common and in-the-open.