Arguably the biggest rivalry in the National League gets its first postseason series...
The Chicago Cubs have been a part of the National League since 1876 (though they were the White Stockings, Colts, and Orphans before adopting Cubs as their name in 1903). The St. Louis Cardinals were founded in 1882 (as the Brown Stockings, because stocking color was apparently the only system anyone had for naming a team back then; they were then the Browns and Perfectos before becoming the Cardinals in 1900) and joined the NL in 1892.
The two teams have been playing one another for 124 seasons, but they have never faced off in a postseason series until now.