What was (is) the purpose of the division line?

I would have to look it up, but I believe 6-on-6 basketball actually started before the division line rule in 1933, which means it's original intent was for 6-on-6. Also, I believe Iowa was the first state to use it, then others adopted it but made modifications. Iowa's was 3 offense and 3 defense, because I remember the defense having to pass the ball to their offensive players across the division line. I'll look up the date on 6-on-6's creation to make sure, but then again, I could be wrong.