It is a question of what makes people do what they do. These somewhat murky waters clear upon examination of the nature of crisis, the standard human condition. Hamlet and Arjuna's crises are strikingly similar, given the thousands of years and miles separating their inceptions. Both are princes who find themselves trapped in horrible circumstance whose only resolution demands the shedding of family blood. It comes from the root dhr , meaning to hold or hold together.
Dharmic action is thus that which sustains the culture.
This is not the culture of ephemeral trappings, but the groundwork through which man lives in the world. At the outset of Hamlet the prince learns of his task. He must kill his uncle, King Claudius, who has just assumed the throne of Denmark upon the death of King Hamlet, Hamlet's beloved father. The dead king returns from the nether regions to inform his son that his death had not been naturally caused as had been supposed, but that he was poisoned through the ear while sleeping. The murderer was none other than Claudius, his brother upon whom the elective monarchy fell.