system
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human
[The Culture] How did the Idirans pose any resistance at all?

The Culture Minds work out and win battles in nanoseconds and the Idirans don't have anything like minds. How did they manage to not be obliterated at once and actually win some battles?
gpt
The Idirans come from a planet of incredibly horrible predators, and they were at the top of the food chain. They were a theocratic warrior species and had been honing the art of war for millennia. They were also biologically immortal and incessantly aggressive. By the time the culture became aware of them, they were already a stage-7 civilisation with an enormous amount of captured space with several other stage-7 and stage-8 allies. The Homomda were one of their biggest allies and were in part, practically on the same tech-level as the Culture.

The Culture had spent at least 8000 years perfecting their own type of utopia - something completely opposite to the hegemonistic and aggressively expansionist Idiran empire. At the beginning of the war, the Culture simply didn't own any war material, and so used Contact as its military fleet. Losses at the beginning were enormous, mainly due to the fact most people in the culture wanted nothing to do with the war. Debates and votes took a lot of time whilst vast expanses of space had to be evacuated from the invading Idirans.

Culture minds themselves (the higher-up ones at least) probably had no doubt about their eventual victory, but couldn't be seen to be aggressive in kind, lest they completely destroy the utopian principles their society was founded on. They retreated, regrouped and coalesced until the Idirans eventually spread themselves thin. At this point (a good thirty years since the war started) they'd had enough time to create war ships and war strategies for actual straight-up fighting. By this time, the Idirans realised they'd underestimated their enemies ability to adapt but also had no idea of the depth of their technical ability. Stuff like being able to hide ships in the corona of a star - such was the excellence of their field technologies.

In short, the Culture could have utterly obliterated the Idirans much sooner, but to do so, would have killed the principles of peace they'd worked close to ten thousand years to achieve, and would have probably been the end of their much-loved society.

The idirans actually did have minds - just slaved ones. When the war was over, the Culture visited Idiran-Prime and installed their own mind, just to make sure everything from then on, was far more peaceful. This probably wouldn't have been possible if done sooner, as it would have seemed like an invasion as opposed to a tactic to ensure future peace.