Simplify the following text for a Grade 11 native English-speaking person.
Original: In the context of Russian Orthodox church history , the Old Believers ( Starovery , ) became separated after 1666 from the official Russian Orthodox Church as a protest against church reforms introduced by Patriarch Nikon between 1652-1666 .
Simplified: In the context of Russian Orthodox church history , the Old Believers became separated after 1666 - 1667 . They split from the hierarchy of the Russian Orthodox Church as a protest against church reforms introduced by Patriarch Nikon .