Beginning with the murder of King Umberto I. of Italy in july 1900 by an italian anarchist, the incidents connected to terrorism rose dramatically in the 20th century. The contributing factors may be the availability of hand held fire weapons and explosives for the public, together with a chance of publicity created by modern mass media. With assassination of Franz Ferdinand , Archduke of Austria and his wife by a serbian member of a political group, an act of terrorism even developed into a world war, amongst other factors, contributing to the Death of more than 10 million people.
Acts of state terrorism were committed by the governments of various dictatorships of the 20th century, including the Soviet Union, Germany, China and Japan, adding at least 150 millions murdered civilians to the death toll of terrorism. (R.J. Rummel: Death by Government)
The IRA is considered to be responsible for teh most sustained terrorist activities of the 20th century. With the increase of air traffic hijackings and other attacks have become a spektakular terrorist act. The most popular internatational terrorist group of the present is Al Quida, which ist also supected to be responsibe for the attacks on both towers of the world trade center in New York in september 11th, 2001.
The Memorial Institute for the Prevention of Terrorism (MIPT) counts a total number of 849 terroristic groups worldwide.