Simplify the following text for a Grade 10 native English-speaking person.
Original: As a General in the United States Army , Powell also served as National Security Advisor ( 1987 â `` 1989 ) and as Chairman of the Joint Chiefs of Staff ( 1989 â `` 1993 ) , holding the latter position during the Gulf War .
Simplified: During his military career , Powell also served as National Security Advisor ( 1987 â `` 1989 ) , as Commander of the U.S. Army Forces Command ( 1989 ) and as Chairman of the Joint Chiefs of Staff ( 1989 â `` 1993 ) , holding the latter position during the Gulf War .