The Phillies–Pirates rivalry, also known as the Keystone Series, is a Major League Baseball (MLB) matchup between the Philadelphia Phillies and Pittsburgh Pirates that began in 1887, when the Pirates joined the National League four years after the Phillies. The rivalry reached its peak during the two-division era (1969–1993), when the teams dominated the NL East, combining for 15 division titles (Pirates 9, Phillies 6) and accounting for more than half of the division's championships. The 1970s were particularly intense, as the two clubs made 10 of 11 NLCS appearances from 1970 to 1980, and each won a World Series during their pennant years—the Pirates in 1971 and 1979, and the Phillies in 1980. Historically, the Pirates had early success, winning the 1909 World Series (the first team to win a championship in a new stadium, Forbes Field), while the Phillies endured a record 16 consecutive losing seasons from 1933 to 1948—a mark ironically broken by the Pirates in 2009. After the Pirates moved to the NL Central in 1994, the teams now meet only twice a year, diminishing the rivalry, but deep-seated regional animosity between Eastern and Western Pennsylvania still keeps the dislike alive among fans.