Complex sentence: The St. Louis Cardinals are one of the most successful franchises in Major League Baseball, and have won 19 National League titles, which are the most pennants for the league franchise in one city, and 11 World Series titles, with the most recent in 2011.
Split into simpler sentences: The St. Louis Cardinals are one of the most successful franchises in Major League Baseball. They have won 19 National League titles (the most pennants for the league franchise in one city) and 11 World Series titles, most recently in 2011.