Why is overpopulation in the real world a threat and how might it foster the Brave New World?

I think overpopulation is only a threat because five percent of the world refuses to share with ninety five percent of the world. When resources become scarce, totalitarian and autocratic states usually follow. People feel the need to protect what is "theirs" and keep the desperate away from their resources. States, like in The Brave New World, strive to stratify the population in order to give the elite what they have become accustomed to.