Family
Family relationships are always messy in Shakespeare's plays, especially when royal families are involved. And by "messy," here doesn't just mean complicated; it means they're bloody, too. In King John, an uncle wants to snuff out his nephew, mothers are accused of giving birth to "bastard" children, and two brothers squabble over land.
Betrayal
From beginning to end, King John is rife with all manner of political double-crosses. Actually, they're usually more like triple-crosses, or even more. For example, King Philip betrays Constance and Arthur when he thinks he can secure a good deal for his son Louis; but then he betrays his new alliance with King John when Cardinal Pandolf brings the pressure of the Church to bear on him.
Loyalty
Hubert sums it up best when he's representing the citizens of Angers: "Sure, we're loyal to the King of England; we just don't know who the King of England is right now." He's got a point: when loyalty is strong in this play, it often leads to horrible things, or almost leads to them. Take Hubert's loyalty to John, for example: it nearly leads him to blind and kill young Arthur.
Even though Hubert, on that occasion, ends up showing a higher loyalty to his friend Arthur by breaking his loyalty to John, we get the impression that, on other occasions, his loyalty to John probably has actually led him to commit horrendous acts.
