The Cubs may have had raciest tendencies in the 50's-60's [though Banks and Williams were beloved and stars and Jenkins came on in mid 60's] but to suggest that Brock was traded to the Cardinals because of this is simply false. I became a Phillie phan in the second half of the 1963 season [they went 56-35 to end the season and then were 90-60 before the '64 collapse so I sure got lots of winning early] and I remember the Brock for Ernie Broglio deal well.
It occurred at the trade deadline, June 15,1964 and the consensus was that the Cubs had gotten the better of the deal. In fact, the Phils have a pre-trade Lou Brock mini lite in Roman Quinn. A player blessed with incredible speed, obvious athletic skills, surprising power for a smaller player and a guy who seems to have maddening inconsistencies. The only difference is that Brock was never injured and Quinn is almost never healthy. But there talent level is quite similar.
Broglio was an established top of the rotation starter and had won 60 games in four years leading up to the trade and was still only 27 years of age. The Cubs had 3 solid starters in Larry Jackson, Bob Buhl and Dick Ellsworth and felt that Broglio would give them a very good 4 man rotation, which was what teams used in those days. Unfortunately for the Cubs, he had arm woes and never regained his former dominance whereas Brock went on to a HOF career.
But if today the Phils dealt Quinn to the Indians for Mike Clevinger [pretty comparable to the 1963 Broglio] most people would think the Phils had made a very good deal. That was the situation then. Please don't misinterpret my comments to suggest that racial reasons didn't play a part, I don't know and it was never discussed at the time. Not to mention that the Cards had their own racial issues in the early 60's, something Bob Gibson referred to often.
However, at the time it was considered a purely baseball related deal and as a Phillie phan I remember thinking the Cards had weakened and not strengthened themselves with the deal. Brock showed almost immediately via his play how wrong I was.
RIP Lou Brock