Simplify the following text for a Grade 8 native English-speaking person.
Original: Al-Qaeda ( or ; , ' , `` the base '' ) , alternatively spelled al-Qaida and sometimes al-Qa ` ida , is a militant Islamist group founded sometime between August 1988 and late 1989 .
Simplified: Al-Qaeda is a militant Islamic group started between August 1988 and late 1989 .