For much of the 20th century, bombings and assassinations have been the tools of ethnic groups fighting for their own nation-states. The tactics were undeniably brutal, and the consequences global. One of the most notable terrorist attacks of the century, the 1914 assassination of an Austro-Hungarian Archduke by a nationalist Serb, ignited World War I.

The aims of these groups could be politically delineated. Bosnian Serbs, for instance, wanted to escape Austro-Hungarian rule and join Serbia, a desire that re-emerged after the breakup of Yugoslavia in 1991. The Irish were striving for independence from Britain, as were the Jews living in what was then Palestine. Disputes about land and power were subject to political negotiation, and for most of these groups, terror ultimately helped them prevail. As Walter Laqueur, a historian, noted in his 1987 book ''The Age of Terrorism,'' ''To succeed, terrorist demands have to be 'realistic' (i.e. limited in character).''

Mr. bin Laden's loosely organized Al Qaeda movement pursues goals far harder to define or satisfy. Experts say it is part of a significant trend in which terrorist groups espouse millennial or religious ideologies that transcend politics or national borders.

In his rambling 1997 interview with CNN, Mr. bin Laden said his jihad against the United States would conclude only when Washington withdrew from Saudi Arabia and ended its ''aggressive intervention against Muslims in the whole world.'' He invoked God and Islamic tradition, and reminded viewers that it was not permissible for non-Muslims to remain as protectors in Saudi Arabia. He makes clear that his targets include the Egyptian and Saudi Governments, deemed insufficiently devout.

''If you look at books written about terrorism 25 years ago, religion doesn't appear,'' Mr. Laqueur said. ''Statistics today show that more than half of terrorist activities are committed for religious or pseudo-religious reasons.''