Executive Meddling: Tezuka wanted to make an epic series exploring the meaning of family and sacrifice. NBC wanted a kid's show. Ironically, this may actually have been a good thing as the compromise they worked out made the story much less depressing and one of the most popular incarnations.
NBC asked that the series be cut from Tezuka's planned 78 episodes to 52, at the insistence of local NBC affiliates who demanded an easy number for programming purposes (one episode every Saturday for a full year). Tezuka agreed. NBC further required that, instead of Kimba maturing over the course of the series as Tezuka wanted, he stay a cub for the entire run and the show have Negative Continuity – this was also an order from local stations in the US, who didn't want to have to show episodes in order (and in fact, they didn't). Tezuka agreed, but then promptly had his animators do whatever they could to subtly undermine NBC's dictates.
Keep Circulating the Tapes: Operative until the late 90's. NBC's license for the original series lapsed in 1978, shortly after Tezuka's Mushi Pro studio went under. So for nearly two decades, the only way to see any of the series was through very early awful-quality VHS tapes, and even then it was just a handful of the 52 episodes produced. The rights to this series – along with the rest of Mushi's properites – were tied up in court for pretty much the entirety of the 80's. Through what can best be described as pure luck, Right Stuf – which already had the rights to Astro Boy – managed to license this series and release it in its entirety.
This still applies to everything else Kimba-related, though. The movie was an exception, but has since gone out of print due to its distributor falling on hard times and letting the license expire.
Money, Dear Boy: This explains why Osamu Tezuka agreed to so many of NBC's Animation Age Ghetto demands. Astro Boy was a big hit in the US and NBC wanted Tezuka to make them another show, this time in color. However, Japan hadn't made the switchover to color broadcasts yet. Mushi Pro wasn't equipped to produce anything in color and didn't have the resources to convert the studio, so NBC said they would pay to convert Mushi to color production, so long as they had say over Kimba. This was the result.
No Export for You: The original manga has yet to see a English-language release; the unfortunate representation of African Natives in this series – and Tezuka's drawings of coloured people in general – seems to be a significant barrier for publishers.
The Other Darrin: There was a re-cut and re-dub of the original Kimba the White Lion in the early 90s, with an unknown VA, Yvonne Murray, playing the role of Kimba. This version isn't as popular as the original Billie Lou Watt dub.