A revolution is a sudden and significant change in the way a society or system functions, often involving a complete or radical overthrow of the existing government or social order. Revolutions can occur for various reasons, such as political, economic, or social grievances, and they are often characterized by mass mobilization, protests, and sometimes violence. Revolutions can lead to the establishment of new political systems, the redrawing of national borders, and changes in the distribution of power and wealth. Some of the most famous revolutions in history include the American Revolution, the French Revolution, and the Russian Revolution.