Simplify the following text for a Grade 7 native English-speaking person.
Original: Rather , it was invoked for the first time in 2001 in response to the September 11 , 2001 attacks against the World Trade Center and The Pentagon in Operation Eagle Assist .
Simplified: It was used for the first time in 2001 when the September 11 , 2001 attacks against the World Trade Center and The Pentagon had taken place .