Simplify the following text for a Grade 6 native English-speaking person.
Original: Brandenburg and Prussia were unified two generations later . Anna , granddaughter of Albert I and daughter of Duke Albert Frederick ( reigned 1568 â `` 1618 ) , married her cousin Elector John Sigismund of Brandenburg .
Simplified: In 1618 the new Duke of Prussia was the Elector John Sigismund of Brandenburg .