The Cardinals–Royals feud (also referred to as the Exhibit Series or I-70 Series) is a Major League Baseball (MLB) championship series rivalry between the National League (NL) Central division’s St. Louis Cardinals and the American League (AL) Central division’s Kansas City Royals.
So obviously the Kansas City Royals Biggest Rivals are the St. Louis Cardinals.
The Cardinals have been in the National League since 1882 when they were known as the Brown Stockings. As one of the American League’s initial expansion teams, the Royals entered the major leagues in 1969.
The last time the Cardinals and Royals met before major league baseball established interleague play in 1997 was in the 1985 World Series. Prior to the World Series, the two clubs had seen various periods of sustained success (as well as several notable droughts).
After winning the 1964 and 1967 World Series and appearing in the 1968 World Series, the Cardinals had a difficult time in the 1970s. By the late 1970s, the Kansas City Royals had established themselves as one of baseball’s top teams, having advanced to the American League playoffs six times between 1976 and 1984, including winning the World Series in 1980.
Inside the early 1980s, the Cardinals resurrected as a pennant challenger, winning the World Series in 1982.