I think diplomacy itself can help gear a country to defend itself by creating powerful allies who will come in a time of need.
At the same time, I do not think there is any justification for war or harming others non-defensively.
The amount of money and human power we piss away with wars and conflict is so sad. Humans are the most advanced and capable complex adaptive systems in the world. Why waste such a precious resource?
Stupidly flippant but likely somewhat accurate answer: x-thousand years of tribal evolution.
With all our intelligence we're still programmed to behave in particular ways, and it takes a lot of effort to even try to break out of it, and that's only possible if you're aware of it - which most people aren't.
Hmm, I think you are correct, and from my perspective, speaking to the idea of human heuristics and biases.
Ironically, I think societies and cultures need long periods of peace (not in an extreme sense, but rather enough peace to allow for safer conflict) to have the time and ability to introspect on their heuristics and biases, as well as integrate other people's perspectives.
Having something to lose, makes it a lot more likely to bring you to reason.
It takes seconds to destroy what it took decades to build.
If someone is pointing a mortar at your house, you want to get rid of the mortar, but you also want to keep your house, so it's likely that you will look for ways to remove the mortar, that don't include it being fired.
At the same time, I do not think there is any justification for war or harming others non-defensively.
The amount of money and human power we piss away with wars and conflict is so sad. Humans are the most advanced and capable complex adaptive systems in the world. Why waste such a precious resource?