Why did Eteocles and Polynices end up fighting each other?

Eteocles and Polynices ended up fighting each other primarily due to a power struggle that arose from Eteocles' decision to seize control of the throne of Thebes. Following their father's death, the brothers had agreed to alternate rule over Thebes, but when Eteocles took power first, he refused to relinquish the throne to Polynices after his term had ended. This act of seizing and monopolizing power led Polynices to gather an army and march against Thebes to claim his rightful position. The narrative in "Antigone" emphasizes this conflict driven by familial betrayal and ambition, showcasing the tragic consequences of their feud, ultimately leading to their mutual destruction. The underlying themes also illustrate the devastating impacts of pride and a desire for power within a family dynamic.