Simplify the following text for a Grade 10 native English-speaking person.
Original: On 3 October 1990 West Berlin and East Berlin were united as the city of Berlin , which then joined the Federal Republic as a state , along with the rest of East Germany .
Simplified: On 3 October 1990 , West Berlin and East Berlin were united as the city of Berlin , which then acceded to the Federal Republic as a state .