A little NFL trivia about the Dallas Cowboys?

A bit of a random question, but a question that has perplexed me this past week: Why are the Dallas Cowboys in the NFC EAST? To be geographically correct, they are hardly on the eastern United States....suffice to say, I am a bit surprised that they are not in the NFC South. I mean, even Tampa Bay and Carolina--two teams in the NFC South--are more east by location than the Cowboys. Anyone got an answer for me? Person with the most accurate answer gets Best Answer.