The term "short 20th century", originally proposed by Iván Berend (Hungarian Academy of Sciences) but 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. World War II was greatly influenced by the outcome of 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, and to the long 18th century, or approximately 1688 to 1815.