Kings are necessary, but -- Dark Ages? High MIddle Ages? Rennaissance? Ancien regime? 19th century?
Then a plot twist suggested that they have balloons. Not as curiosities either -- a child suggests using them in a way that argues for their being common knowledge. Which settles that. (Trains? Telegraphs? What else will slither in and change things?)
And then I just have to wrestle with exactly how legitimate our tyrant-king is. Certainly he's the sort who would take the throne by violence and treachery if necessary, but he might not need to. . . .