When did division titles in baseball come into effect?

In MLB, that was 1969.

Starting in 1969, the teams in both the American and National Leagues were broken up into two divisions. This coincided with expansion as two new teams entered each league making the number of teams in each league 12 instead of 10. The Kansas City Royals and Seattle Pilots (now the Milwaukee Brewers) entered the AL and the San Diego Padres and Montreal Expos (now the Washington Nationals) entered the NL.