Answer: The area was nearly vacant for remodelling.
The flight that crashed into the Pentagon was American Airlines Flight 77, which was originally intended to go to Los Angeles. The crash killed all 64 people on board, including five hijackers and six crew, as well as 125 people in the building. However, the damage to the Pentagon was not as extensive as it could have been, as remodelling had recently been carried out and the area was nearly vacant.