On a day in 1993, there was an attempted attack on the world trade center. The terrorists placed explosives in the basement of the north tower, and hoped to knock it into the south tower, but it didn't fall, but six people died.
on September 11, 2001, a hijacked plane was crashed into the twin towers.
A third plane crashed into the pentagon and another into a field in PA. It was believed to be headed for the White house or the capital, but the passengers fought back the hijackers and stopped them.