From The Art and Popular Culture Encyclopedia
The short twentieth century, defined by Eric Hobsbawm, a British Marxist historian and author, refers to the period between the years 1914 and 1991.
That period begins with the beginning of World War I, and ends with the fall of the Soviet Union. The chain of events represented such significant changes in world history as to redefine the era:
It started with World War I, which caused the end of the German, Ottoman, Austro-Hungarian and Russian empires and kingdoms. World War II was a result of the World War I. The Cold War was a result of World War II and ended with the fall of the Soviet Union.
The term is analogous to the long 19th century, also coined by Hobsbawm, denoting the period 1789 to 1914.