Simplify the following text for a Grade 7 native English-speaking person.
Original: Rebel forces entered and took the city in 1990 , forcing the then President of Somalia , Mohamed Siad Barre , to flee in 1991 to Kenya .
Simplified: Rebel forces entered and took the city in 1990 . They forced President Mohamed Siad Barre to resign and leave the country in January 1991 .