The attack on the World Trade Center Tuesday was not the first on the 110-story twin towers.
In February 1993, a truck bomb exploded there, killing six people, and displacing business in the complex for six months. Six Islamic militants were convicted in the bombing, and sentenced to life in prison. The attack was meant to pressure the United States to stay out of the Middle East and curb its support of Israel.
Until Tuesday's attack, the most serious case of terrorism in the United States occurred in April of 1995, when a truck bomb exploded at a federal government office building in Oklahoma City, killing 168 people. Timothy McVeigh was convicted of federal murder charges and executed in June.
In a more recent terrorist incident, the USS Cole was refueling in Yemen's port of Aden in October of last year when a small boat pulled alongside it and detonated explosives, killing 17 U.S. servicemen. U.S. authorities suspect Saudi exile Osama bin Laden was responsible for the incident.
In August 1998, bombings at the U.S. embassies in Kenya and Tanzania killed 224 people. Osama bin Laden is again blamed.
In another terrorist incident on African soil, Congo-based Rwandan rebels killed two Americans along with six other foreign tourists in Uganda in an attack in March 1999.
In one of the worst cases of terrorism in the air, 270 people were killed when Pan Am flight 103 exploded over Lockerbie, Scotland, on a flight from London to New York in December 1988.
Meanwhile, the Middle East has seen its share of terrorist activity directed against Americans.
In Saudi Arabia in June 1996, an attack on the U.S. military complex at Khobar Towers in Dhahran killed 19 Americans. Members of a Saudi militant group were indicted for the attack. Seven months earlier, a car bomb detonated at U.S. military headquarters in Riyadh, killing five American service personnel.
In June 1985, Shiite Muslim gunmen seized a TWA passenger jet, forcing it to Beirut. They demanded the release of 700 Arabs held by Israel. A U.S. navy diver was killed and 39 Americans were held until their release a month later after Syrian mediation.
In October of that year, a disabled American Jewish man, Leon Klinghoffer, was killed by Palestinian militants were had seized the Italian cruise liner Achille Lauro.
One year earlier, in September 1984, a car bomb at U.S. embassy annex in east Beirut, killed 16 and injured the ambassador.
In December 1983, Shiite extremists set off car bombs in front of the U.S. and French embassies in Kuwait City, killing five people and wounding 86.
In October of that year, Shiite suicide bombers blew up the French military headquarters and a U.S. marine barracks in Beirut, killing 241 marines and 58 French paratroopers.
In April 1983, suicide bombers blew up the U.S. embassy in Beirut, killing 17 Americans.
And in November 1979, Islamic students stormed the U.S. embassy in Tehran, Iran, holding 52 Americans hostage for 444 days.