You don't need to be past the carrying capacity of the environment to spark a war. Carrying capacity refers to basic survival. Wars can be fought over
any scarcity, even if it's not relevant to survival, even to protect against future scarcity.
Post-scarcity theories hypothesize a world where "scarcity"
can't be a factor. Not "currently isn't". Where you can eat and drink and entertain yourself in whatever manner you see fit without any limitations whatsoever, and without any concept of "wealth" or "income" to justify it. Even Star Trek isn't quite there; they have certain budgetary restrictions on things; they can't just "print off" another starship, for instance, meaning starships are suffering issues of scarcity.
The current world isn't even remotely post-scarcity. Scarcity is a real, massive issue. Even in the US, as I pulled out for another thread, something like 15% of households
can't afford enough food.