It was not written anywhere in the league's bi-laws that blacks couldn't play with whites. It was what was called a Gentleman's Agreement, an unwritten rule that no one dare challenged. Upon Landis' death ini 1944, he was replaced as commissioner by Happy Chandler (a fiction writer could not create better names). Chandler was approached by many black players and he, in clear conscience, could not tell them to their faces that they couldn't play with the white players. He was open to integration, but the owners were not (the so-called gentlemen). He had all sixteen of them vote on whether to integrate. Only one owner, Branch Rickey (one of my personal heroes), the manager of the Brooklyn Dodgers, voted for integration.
Branch Rickey went on to do this on his own. He acquired Jackie Robinson and had him play in the Dodgers AAA club in Montreal because Canadians aren't as screwed-up about race as those of from the land of the free are. Every baseball fan knows all about what Robinson went through. Rickey chose him as the first black player not only for his playing abilities but for his personal character. He faced death threats, threats to his family and insults ad nauseum not only from players and fans but sometimes from his own teammates. Rickey continued to acquire black players building his team to playoff berths in 1941, '47, '49, '52 and '53.
The teams that integrated early are the teams that dominated the sport for the next two decades. It is with much regret that I point out that the very last team to integrate was the Boston Red Sox (my favorite team) with Pumpsie Green in 1959. The city of Boston today is still very segregated so this should not be a surprise to anyone who has ever lived there. It wasn't the curse of the Babe that prevented this franchise from winning for so long; it was the stupidity of racism. The team was so racist in this era that you couldn't be on the team if you weren't Irish or Italian at given times. For awhile only Catholics were allowed on the team. I started following the team in 1976, not too long after this era. Jim Rice was my favorite player as a kid. Rice has claimed many times that the specter of racism was over by the time he played at Fenway. I am never tired of hearing that and a little grateful. I don't know how I would have grown up thinking about race without seeing such a spectacular outfielder playing the flies off the Green Monster as Jim Rice.