(i) A fictional premise with consequences that include military conflict.
(ii) An interest in war as such.
(i) Premise: humanity spreads into the galaxy and encounters other races.
Consequences: two interstellar spheres of influence must adjust their borders (The People Of The Wind);
another race is aggressive and wants the same territory (sea and space battles in Ensign Flandry).
Premise: history goes as badly as possible, specifically modern slave-owning culture survives and thrives.
Consequence: the Draka conquer and enslave everyone else.
(ii) Jerry Pournelle's future history and other series.