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I remember playing a strategy game as a kid where the map was divided between 4 kingdoms, and duels took place for each land plot in sequence. That is, in our case, Crimea, for example, cannot attack Lviv or Kyiv because other lords are in the center :D, and so on (well, maybe at least after the entire map has been distributed and there are no more free plots left).
Maybe we could refine something in this vein? It would be a nice visual effect in addition to the gameplay, showing the expansion of your kingdom (or its defense). For example, losers could take new and new lands until they are pushed back to the borders and have nowhere else to run. In turn, the principle that Vic wrote about above would be logical: the attacker claims a specific plot from a neighbor without risking their own, and the defender, in case of victory, defends their land and gains the right to attack in the next round according to the same rule. Maybe give each player the right (again, when the entire map has been distributed) to make one attack per turn (i.e., they can attack a neighbor and defend their land from another at the same time). From a strategic point of view, this is logical, but in terms of time and the possibilities of playing in one turn, it might be too much. In general, what do you think?