It seems like you’re explaining the actions of kings with the preferences of peasants (and I am very unconvinced that a victorious war was better for the average peasant than peace), and I don’t see that as particularly persuasive.
Starving peasants revolt. Kings don’t like revolts. Using starving peasants as soldiers to conquer new land is a way to divert peasant revolt by promising them the new land. And the king kills 2 birds with 1 stone, since starving peasants die killing neighbouring rivals. I’m not certain that’s how it happens, but it’s plausible and it solves all your qualms.
Starving peasants revolt. Kings don’t like revolts. Using starving peasants as soldiers to conquer new land is a way to divert peasant revolt by promising them the new land. And the king kills 2 birds with 1 stone, since starving peasants die killing neighbouring rivals. I’m not certain that’s how it happens, but it’s plausible and it solves all your qualms.