Simplify the following text for a Grade 12 native English-speaking person.
Original: From 1949 to 1990 , the main political parties were the Social Democratic Party of Germany ( SPD ) and the Christian Democratic Union ( CDU ) , with its `` sister party '' , the Christian Social Union of Bavaria ( CSU ) .
Simplified: There is a multi-party system that , since 1949 , has been dominated by the Christian Democratic Union ( CDU ) and the Social Democratic Party of Germany ( SPD ) .