The central thematic conflict on William Faulkner's Barn Burning is family loyalty versus social appropriateness, and the pressures of blood ties versus the chastising of behaviors within one's own family.
In this way the central thematic conflict is a modern dilemma for Sarty. In the story, Sarty has to choose between remaining loyal and keeping the secret of his father, which is to burn other people's barns as an act of sadistic enjoyment. The father intends to initiate Sarty in this practice and invites him to watch him do it.
Sarty's modernist dilemma consist in deciding whether he is going to perpetuate an abhorrent conduct only for the sake of the blood ties that connect him to his father, his primary care provider. The second option: Give his father in to the Major of Spain, and destroy any chance of this happening again in the future, even if it means telling on his father and getting him in trouble.
All this was very hard for a young boy whose only life has consisted in watching his father commit these acts as if nothing wrong was with it. It is a form of brainwashing that Sarty has almost fallen for. Yet, we know that the difficulty lays primarily in the boy's feeling of loyalty to a father who is breaking the law, and the boy's coming of age into recognizing that what his father is doing is wrong, and one must man up to the fact and face the consequences.