Was thinking about where a story went in history because it involved a war. When countries are unified under a single monarch, that would limit their possibilities. Especially if the monarch had real clout.
Except that, hmm, it would not actually stop war. It would make it a civil war. Or a semi-civil war. Wars of independence perhaps, like Belgium seceding from the Netherlands. Of course, its exact status probably depends on whether the monarch supports the side that opens fire, or the one attacked. (I note that in medieval times, you could add two realms together by matrimony -- sometimes -- that's how France acquired Champagne -- but not so much in modern times, where the French king's claim to the Spanish throne was passed to his second grandson, who had to renounce any rights to the French throne, to avoid such things.)
Still putting the war earlier. It might not make too much of a change, but it would make enough to affect the story, if the kingdoms were not, in fact, completely separate.
Well, except for the alliances. I think the hero's country is coming to the support of an ally.