After the establishment of a baseball league of four teams in Athena City in 2125, Galileo City quickly followed suit by establishing its own league in 2127 and a rivalry of words began between the two planets over which world hosted the superior baseball teams. Most of this talk was conducted in the newspapers and periodicals of the worlds but the people on each planet firmly believed that theirs was superior.
Of course, what existed was two different type of baseball with the Athenian league playing using American League rules including the Pinch Hitter while the Galilean League played using National League rules. As such, their game play was different and it was difficult to really tell which was superior.
The owners of the eight baseball teams came together in early 2129 and decided that an exhibition series should be held between the champion of each league to determine for the fans which planet had the best. It was exhibition because the leagues, at the time, were unaffiliated and no purse was available to share out to the winner. Still, it would please the fans and the winners of each league faced each other in 2130, a matchup between the Galileo City Steers and the Athena City Sand Dollars.
In what was to be a best of five series, the Steers won the first game 5-3, mostly on the two errors committed by the Sand Dollars. But that would be their last win as the Sand Dollars went on to win the next three games. It took three weeks to play the series given the travel times between the two worlds and Galileo City hosted two of the games while Athena City hosted the last two.
But all the owners were pleased with the result, even those on Galileo despite the Steers loss. Every game sold out and viewership totaled higher than any other regular or post-season game. Both the Steers and Sand Dollars saw significant profits from the staging of the series and it became inevitable that another would be hosted the following year.
With the addition of the Japanese League in 2132, it was decided that some form of official governance should be added to the sport and Colonial Baseball was created to oversee the addition of new teams as well as the regulation of its subsidiary leagues.
The new series was to remain a best-of-five competition with three games hosted on the first world and two on the other, the home field advantaged determined by a coin flip. However, because of a poor showing by the New Onojo Sea Lions in 2133 in which all three of the games hosted in Athena City were won by Sand Dollars, the series never even made it back to Yamanashi for play. Because of this, the Republican Series was expanded to a best-of-seven so that at least one game would be hosted on the opposing world.
While this seemed generally fair and reflected the structure of the World Series on Earth, a string of 4-1, 4-2 games between 2135 and 2139 left the fans on each planet represented by a team in the series wanting to see more play on their worlds. Because of this the series was expanded yet again to a first-to-seven format, significantly lengthening the time it took to play the series but finally meeting the fans demand for more home games.