Simplify the following text for a Grade 8 native English-speaking person.
Original: It was started in 1988 by joining the Liberal Party , which had been a powerful political party in Britain in the 19th and early 20th centuries , and the Social Democratic Party , which had been formed from the Labor Party in 1981 .
Simplified: The party was formed in 1988 by a merger of the Liberal Party and the Social Democratic Party .