What are Creon's principles that lead to the tragic ending in Sophocles' Antigone ?
Several of Creon's principles led to tragedy. However, the one principle he held that is the most damaging is the belief that as king he is sovereign. He refuses to listen to anyone's council but his own.
One place we see Creon refusing to listen to anyone's council is when he is chastising Antigone. After Antigone explains that she buried her brother because she sees the gods' laws as being higher than Creon's, Creon argues that he would not be fulfilling his role as a man if he were to let her get away with her deed, as we see in his lines, "Now I am no man, but she is a man, if power lies with her with impunity" (498-500). We even further see him refuse to listen to not just Haemon's point of view, but the entire city's as expressed by Haemon after Creon decrees Antigone's punishment. He even goes so far to show his tyrannical nature as to say that he will not let the city tell him how he should rule, as we see in his line, "The city will tell me how I ought to rule it?" and even "Should I rule this land for myself or for others?" (745-747). Creon even refuses to listen to Tiresias's warnings, particularly the warning that Creon is bringing destruction to the city for dishonoring the gods, just as both Antigone and Haemon already argued.
His belief that the king is sovereign also leads to holding the principle that the state is infallible. Creon has decreed Polynices to be the traitor to state, which is why he is denied burial. However, according to mythology, Oedipus left both brothers to rule over the kingdom equally. The brothers agreed to take turns and alternate holding the throne each year. However, after the first year, Eteocles refused to pass the crown on to Polynices and had him exiled. Polynices of course battled against whom we can see as his tyrannical brother for the crown, resulting in the deaths of both brothers. Ironically, Creon views Polynices as the traitor simply because he battled against the ruling king. However, which brother was in the wrong is really unclear ("Polynices"). Was Eteocles trying to protect the state from his foolish and tyrannical brother? Possibly. Or was Eteocles acting in his own self-interests and therefore Polynices was trying to rescue the state from a tyrant? Even more possible. If the later is the case then, ironically, Creon's principle of holding the state as the highest authority has made him side with a tyrant, making himself act tyrannical as well.
Hence we can see that the principles Creon held that led to his demise were that the king is the highest authority and that the state is infallible. At the time that Sophocles wrote the play, Athens was a democracy ("Historical Context"). Therefore, it can be said that Sophocles used Creon's dictatorial nature to warn against the dangers of tyranny.
Creon believed that the state was greater than the individual. This can sound strange to a modern audience brought up on the rights of the individual. However to the ancient Greeks this would have sounded entirely reasonable. Thebes had been under attack and thus the stability of the state was prized more than the rights of the individual. Paradoxically, the rights of the individual can only be safeguarded in a stable society. Thus Creon, in his own way, believed that he was doing the right thing in punishing Antigone who was behaving in a manner that could foster anarchy and ultimately destabilize the whole state; while Antigone believed that she was right in placing god-given laws above human laws. The clash of both sets of principles, embodied in these two characters, and which is perhaps at the heart of any civil war, led to the tragic ending.