The Mississippi River is accepted as one of the dividing lines of the United States.
Resolves YES for any of the following teams winning the World Series in 2025:
Atlanta Braves
Baltimore Orioles
Boston Red Sox
Chicago Cubs
Chicago White Sox
Cincinnati Reds
Cleveland Guardians
Detroit Tigers
Miami Marlins
Milwaukee Brewers
New York Mets
New York Yankees
Philadelphia Phillies
Pittsburgh Pirates
Tampa Bay Rays
Toronto Blue Jays
Washington Nationals
The Cardinals and Twins were tricky to place because St. Louis and Minneapolis are both on the river. However, both home parks are situated west of the river, so they are considered part of the western side of the league for this market.
1,000Update 9/2:
Of the 17 teams listed in the original post, if the season were to end today, the following teams would make the postseason:
Toronto Blue Jays
Detroit Tigers
New York Yankees
Boston Red Sox
Milwaukee Brewers
Philadelphia Phillies
Chicago Cubs
New York Mets
That's 8 of 12 playoff teams. Subject to change prior to season's end, but it would definitely skew the chances if these remain unchanged.