The Athletics left Kansas City in 1967 and began a dynasty shortly thereafter with three consecutive titles in the early 70s. The new Royals began battling them for the Western Division title throughout the 70s.
The A’s and Royals were the top two teams in the division in 1973 (A’s took the division), 1975 (A’s again), 1976 (Royals), and 1980 (Royals, by a big margin). The A’s beat the Royals under the 1981 playoff format, and the Royals finished a distant second to the Bash Brothers A’s in 1989, missing the playoffs despite having the third-best record in baseball.