Theatre (warfare)
Some wars, such as the Franco-Prussian War, are fought in one theatre. Many wars, for example the Seven Years' War have been fought in many different theatres. There were many theatres in World War I and World War II. The Napoleonic wars were the first multi-theatre war in modern times. The use of the word "theatre" for war was first seen in the book "On War" by Carl von Clausewitz.