What do war and geography have to do with each other?

Answer 1

maybe topography is more apropos than geography.

Land terrain and water bodies determine where guerrilla warfare is feasible as well as what military strategy is optimal or possible. You could call that geography.

That's physical geography. There's also human geography, who lives where and travel routes. If you have too many people, like China or India the leaders are more willing to use war as a population control. If you have too few people compared to potential enemies, war can be suicidal, as you can't field a large enough military for defense, much less an offensive war.