MLB
Championship eras
Era presets are tied to structural changes in the postseason format or the league's footprint. They are not arbitrary decades and they are not defined by which franchise happened to win.
Default analytical range
1995–present
Wild Card Era (combined)
The analytical default combines both wild-card eras because each season ends with one World Series champion decided on the field under a stable core structure.
It is a useful modern baseline, not a claim that the single and second wild-card postseasons are identical in format.
Era definitions
Dead-Ball Era
The modern World Series began in 1903 in an era of low-scoring, contact-oriented baseball played almost entirely east of the Mississippi River.
An epicenter from this period reflects the sport's original American League and National League footprint, not a nationally distributed league.
Boundary basis: 1903 first modern World Series through 1919, the last dead-ball-era titleLive-Ball Era
A livelier ball, Babe Ruth's home-run era, and the Yankees' rise defined this period, still within the sport's original two-league, sixteen-team footprint.
The New York-heavy geography of this era is a real competitive pattern, not a data artifact.
Boundary basis: Live-ball rules begin 1920; Jackie Robinson's debut is 1947Integration Era
Jackie Robinson's 1947 debut began the sport's integration; the same sixteen franchises still played in the same core cities through the decade of the 1950s.
Geographic concentration in the Northeast and Midwest persisted even as the talent pool nationalized.
Boundary basis: Robinson's debut in 1947 through the last season before 1961 expansionExpansion Era
Franchise relocations (Dodgers and Giants to California in 1958) and the first rounds of expansion teams began pushing MLB's footprint west and south.
This era captures the sport's first real geographic diversification beyond its founding cities.
Boundary basis: 1961 AL expansion (and the 1958 California moves) through 1968, the last season before divisional playDivision Play Era
Divisional play and the League Championship Series, introduced in 1969, added a postseason round before the World Series while the champion remained a single undisputed winner.
The longest era in the dataset, spanning free agency, further expansion, and the 1994 strike that cancelled that season's World Series.
Boundary basis: Divisional play begins 1969; the era ends with the 1994 strike seasonWild Card Era
The wild card, introduced for the 1995 season after the 1994 strike, added a fourth postseason team per league and reshaped the path to the World Series.
Champography's default modern range begins here because the postseason structure that produces the champion is coherent through the present.
Boundary basis: Wild card introduced for the 1995 season; second wild card added starting 2012Second Wild Card Era
A second wild card team per league, added starting with the 2012 season, expanded the postseason field to ten teams and introduced a single-elimination wild card game (later a best-of-three series).
This era is included in the broader modern range alongside the single-wild-card period because both produce one undisputed World Series winner.
Boundary basis: Second wild card added for the 2012 seasonWhy structural eras matter
A geographic comparison is easier to interpret when the underlying postseason format is reasonably stable. The two wild-card eras are therefore separate presets, even though both are also included in the broader modern analytical range.
Era boundaries do not make the teams on either side incomparable. They give the user a historically defensible starting point and make changes in the map easier to connect to changes in the sport itself.