Simplify the following text for a Grade 9 native English-speaking person.
Original: It was adopted on March 20 , 1989 , almost two years before the reestablishment of Lithuania 's independence following the end of the Soviet Union . Before its readoption , the flag had been used from 1918 until 1940 when Lithuania was occupied and then annexed by the Soviet Union .
Simplified: The Flag of Lithuania that is used today was adopted by the Council of Lithuania in 1918 and re-adopted in 1989 .