Simplify the following text for a Grade 11 native English-speaking person.
Original: He served as the President of Socialist Republic of Serbia and Republic of Serbia from 1989 until 1997 in three terms and as President of the Federal Republic of Yugoslavia from 1997 to 2000 .
Simplified: He was President of Serbia from 1989 to 1997 and then President of the Federal Republic of Yugoslavia from 1997 to 2000 .