Did you think it was kind of weird that the majority of the first 20 or so lines of this play are about a king and a kingdom that are basically never mentioned again? Well, it's not a mistake. The Duchess of Malfi opens with a description of a particular model of power, which is then contrasted against the corrupt model seen in the various courts of Italy.
Webster's obviously got a deeply cynical view of the court, and that view extends outwards to the ways in which he portrays relationships you wouldn't think of as political. The Duchess's relationship with her brothers or the Cardinal's relationship with Julia are, at first blush, domestic, but are ultimately governed by the same power dynamics that the court run by.
Questions About Power
How is that, as a single woman in 16th-century Italy, the Duchess has political power?
Does power end up being the most important thing? Both the Cardinal and Ferdinand have plenty of power, but they both end up dead.
Do you think that, with the Cardinal and Ferdinand out the way and with the Duchess's Sprog #1 set to inherit her power (presumably with Delio helping him), the court will stop being so corrupt?
Do you think the Duchess and Antonio have a totally equal marriage, or does one of them have more power than the other?
Chew on This
Although the Duchess herself is virtuous, her secret marriage eventually lowers her people's opinion of her and thereby hurts the ruler-subject relationship. Therefore, the Duchess fails as a sovereign when she marries Antonio.
In repeatedly relying on her title and rank as her source of power—falling back on her position within the established social system—the Duchess ultimately undercuts her own desire for freedom from that system.