Sun Tzu has the right idea, he recommends only attacking if you're 6 times the strength of the other side. Less than that and it's too risky (defenders have a lot of inherent advantages).
So if the different sides are somewhat evenly balanced, it's not in anyone's interests to to on the offensive. Offensives only happen if one side (perceives themselves to be) much stronger than their opponent.
Nice explanation, and the contradiction kind of blows away. Or does it? Strength everywhere seems to guarantee peace, but only on certain time scales. It's like playing go, where one should not throw oneself at strength. Yet turn by turn, the board shrinks, and conflict is inevitable. Perhaps strength does kind of tend to minimize the total amount and duration of conflict though
Does the real world have this "shrinking turn-by-turn" mechanic though? It seems to keep expanding, if anything. There are more people, more things, more resources, more complexity each year. That's where the risk is coming from: new sources of power supplanting the old ones.
There's not more territory in any meaningful sense though, and without territory there are no resources. Consider the WW2 era German interest in lebensraum, the Japanese interest in the northern resource region of Siberia ( https://en.wikipedia.org/wiki/Kantokuen ). Since WW2, in theory borders are supposed to be basically frozen and war is technically illegal, but clearly Russia would like to annex something extra. More subtly there are all the soft-power machinations or straight up proxy wars that are energy/resource related, and typically wherever one great power has influence they'll try to freeze out others. Looking forward further, there's only one moon, one solar system..
