I have a similar theory as to why rapidly growing companies become toxic environments (of which politics and turf wars are a symptom). When a company is small and has a low profile, its employees are in it for the company. They believe in the product or service that the company is creating, and but into its mission.

When the company becomes successful and starts to grow, it starts to attract people who don't really care about the company and its mission—they are in it only for themselves. They only want to improve their lot, and are willing to play politics and backstab as required to get ahead..

If the company is only growing slowly, they can weed these types out during the interview process. But if they are growing quickly, they don't have time to interview properly and slowly and surely the company is transformed from a cooperative, mission-driven organization to one where employees are fighting against themselves.

Unfortunately these politically minded types are the ones who quickly rise up the ranks, and once most of the top areas of the company are populated by assholes, there is no cure.