what was the major theme of the persian war

I think Pride and revenge are major themes. Even the strongest of nations will be defeated if it allows arrogance and pride to over-ride its government. Greece did not only wound the armies of Persia with her earlier defeat; Persian pride was wounded as well, and a thirst for revenge is clouding Xerxes' judgement. He also believes that his is an unbeatable foe for the Greeks due largely to the fact that his armies put down rebellions in Egypt and Babylon. This gives him a false sense of reality and makes him think that he can lead his forces to victory over any enemy. Unfortunately, his pride has blinded him to the realities of battle. This is when the ghost of Darius admonishes his son. He tells that he has overweening pride and has been warned by the voice of God to cease attacking Greece.

The main reason for the attack on the Greeks is revenge. Xerxes is angry about being vanquished by the Greek armies and lets this anger fester, so that soon it clouds his judgement completely. A sub-theme in the play is that of the foolishness of acting out of revenge, or seeking vengeance. However, Darius tells us that seeking victory out of vengeance can never succeed and only brings more death and loss.