Hotspur more than anything else, has a code of honor that is mostly tied up with his family and what he believes is just. In one of the first scenes that we see him in, King Henry IV confronts him, and more or less orders him to cut off contact with a family member, who has married the daughter of Glendower, one of his enemies. Henry IV feels that loyalty to the King, and the state should come above loyalty to family, a thought which Hotspur ultimately disagrees with. He values loyalty to family over loyalty to the King, and thus joins in Glendower and companies plot to overthrow Henry IV. Given the legitimacy issues tied up with the death of Richard, Henry IV’s predecessor this is an interesting decision to make, given the complications