The conflict between "the crows" and "the wildlings" in Game of Thrones is a major part of the plot throughout the show. The crows hate the wildlings. The wildlings hate the crows. Clearly, centuries of fighting each other have caused them to have very strong hatred for one another. They killed my family, they killed my brothers, etc.
But...why did they start fighting in the first place? It's alluded to on one than more occasion that the wall wasn't built to keep out wildlings, it was built to keep out white walkers. If that's the case, then what caused the first conflict between the wildlings and the Night's Watch? Why, when some wildlings tried to cross through the wall to the south, did the Night's Watch first stop them from doing so?
The mystery behind this conflict has caused me to ponder some theories, but I just want to know if there is something simpler that I'm missing.