WASHINGTON — Terrorism as a tactic of warfare became a serious problem in the 1960s, when Latin American leftists and then Palestinian extremists seized hostages and hijacked planes to squeeze concessions from local governments. In the years since, terrorist acts have grown ever more lethal. Their goals have grown international in scope, and terrorism has become the leading threat to U.S. national security.
"This kind of terrorism is the face of war in the 21st century," said Bruce Hoffman, terrorism specialist and director of the Rand Corp.'s Washington office.
Ironically, the success of counter-terrorism efforts, particularly by the United States, has forced extremist groups to become more ingenious. "Tragically, what happened in New York and Washington is a reflection of the progress we've made against terrorists," Hoffman said. "With new protective security, we've forced them to act in increasingly sophisticated ways. They could no longer get a truck into the Pentagon or the World Trade Center, so they had to find another way. And they did."
Many of the turning points in terrorism over the last four decades were marked by attacks on American facilities and personnel, causing damage that still shapes U.S. foreign policy.
The first mass hijacking occurred in 1970, when the Popular Front for the Liberation of Palestine seized control of two American planes and one Swiss airliner, all bound from Europe to the United States, to punish the United States for supporting Israel. The Pan Am, TWA and Swissair planes were blown up on the ground in Jordan and Egypt.
After taking over the U.S. Embassy in Tehran in 1979, Iranian revolutionaries carried out the first prolonged mass seizure of hostages--an event that still shapes relations more than two decades later. The 52 American hostages were held 444 days during a national drama that introduced the yellow ribbon as a symbol, as American as apple pie and baseball.
In 1983, terrorists bombed the U.S. Marine compound in Beirut, causing the largest loss of U.S. military personnel in a single event since the Vietnam War. The blast, which killed 241, was carried out by Muslim militias after U.S. warships intervened in Lebanon's civil war. It still serves as a rallying point for Americans who oppose using U.S. forces as international peacekeepers.
In 1983 and 1984, Islamic extremists in Lebanon masterminded the bombing of U.S. embassies in Lebanon and Kuwait, killing dozens and prompting the United States to fortify American diplomatic missions, effectively converting them into fortresses.
But again, it wasn't enough. In 1998, terrorists linked to Osama bin Laden bombed embassies in Kenya and Tanzania simultaneously, killing 224 and wounding thousands.
The most sensational act of airline terrorism came in 1988 with the midair bombing of Pan Am 103 over Lockerbie, Scotland. The blast claimed 259 people aboard the Boeing 747 and 11 on the ground. It led to stepped-up security measures at U.S. airports, but they apparently were not stringent enough to prevent Tuesday's acts.
Terrorism came to U.S. soil for the first time in the 1993 bombing of the World Trade Center, which killed six and injured 1,000. The mastermind was Ramzi Ahmed Yousef, a Pakistani militant trained in Afghanistan. Yousef was captured in 1995 in Pakistan. When he was brought to New York for trial, he bragged to FBI agents that he could have destroyed the complex if he'd had sufficient funds and equipment.
The largest terrorism plot concerning aviation was Yousef's scheme to blow up 11 American airliners over the Pacific in 1995. Code-named Bojinka, or "the explosion," it was uncovered on a computer disk in Yousef's Manila apartment.
Abroad, terrorism turned ever nastier. In 1995, terrorists used chemical weapons for the first time when Aum Shinrikyo, also known as the Aum Supreme Truth, simultaneously released the chemical nerve agent sarin on several Tokyo subway trains. Twelve people were killed and up to 6,000 injured.
Last year, a suicide attack on the guided-missile destroyer Cole killed 17 sailors and wounded 39 as the Navy vessel was docked in Yemen.
Despite the long and bloody history of terrorism against the United States, America is more vulnerable today than ever, U.S. counter-terrorism experts argue.
"As we learned today, the battlefield for America is now everywhere," Hoffman said.
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Oct. 1983: A suicide car bomb attack on the headquarters of the U.S. military peacekeeping force in Lebanon kills 241 American personnel.
March 1985: U.S. journalist Terry Anderson is kidnapped in Lebanon. He is released in Dec. 1991.
April 1985: A bomb explodes near a U.S. air base in Madrid, killing 18 Spaniards; 82 are hurt, including 15 Americans.
June 1985: Four U.S. Marines and two American businessmen are among 13 people killed in a machine-gun attack on a cafe in San Salvador.
June 1985: Hijackers seize a TWA jet en route from Athens to Lebanon. A U.S. serviceman is killed.