 Within this time, the Cubs have won 17 National League pennants, 3 World Series championships, 3 pre-World Series Championships, and tied for 2 pre-World Series Championships.By virtue of their pennants and playoff championships, the Cubs can claim to be the best team in baseball in eight different seasons.The Cubs have been members of three organized leagues, beginning with the amateur National Association of Base Ball Players in 1870, followed by three seasons in the professional National Association of Professional Base Ball Players, and the National League since 1876.