FifthView
Vala
It's a fun but fruitless exercise to talk about what did not happen in history. It's hard enough to figure out what *did* happen. But standing armies and castles can and do go together. The Byzantines are but one example.
Unless the story is specifically set in a historical period on Earth, or perhaps on an alt-Earth, the question of what did or did not actually happen sometimes troubles me. Fantasy worlds are fantasy worlds. The OP did not seem to me to suggest that these countries are strongly Earth-like, even if asking for some real history parallels to use as a general guide for potential effects. Plus, magic played a role in this fantasy setup, so it's always possible that magic may have played a role similar to whatever role gunpowder played in our own history re: castles and such. (Or even a more extreme role and set of consequences.)