Organizational in-fighting. Typically one group needs another group to do something but the ignorant bully leading the other group refuses to help because he is lazy or wants to guard his turf. The war typically ignites in a meeting where both sides pound tables, scream and yell, with one party eventually storming out and retreating to his cube with hurt feelings. Eventually both sides calm down and agree on a terrible compromise that protects everyone's turf at the expense of making the product more complex and confusing to the customer.
Don't waste your time trying to do that the right way. We tried that before and the other team went to war with us on it. So now we do it the worst possible way to accommodate them.