What angers Antigone at the beginning of play?

At the beginning of the play "Antigone" by Sophocles, Antigone is angered by the decree issued by her uncle Creon, the King of Thebes. Creon has declared that her brother Polynices, who fought against Thebes in a civil war, is to be left unburied and considered a traitor. Antigone believes that this is a violation of divine law and familial duty, and she is determined to defy Creon and bury her brother.