While the Idirans universally assumed that having made their point the people in the Culture would back down, a few of the Idiran policy-makers anticipated that, should the Culture prove as determined as a "worst possible" scenario projected, a politically judicious settlement might be arrived at which would save face and have advantages for both sides. This would involve a pact or treaty in which the Idirans would effectively agree to slow or limit their expansion for a time, thus allowing the Culture to claim some — but not too much — success, and provide the Idirans with (a) a religiously justifiable excuse for consolidation which would both let the Idiran military machine draw breath and cut the ground from beneath those Idirans who objected to the rate and cruelty of Idiran expansion, and (b) a further reason for an increase in military expenditure, to guarantee that in the next confrontation the Culture, or any other opponent, could be decisively out-armed and destroyed. Only the most fervent and fanatical sections of Idiran society urged or even contemplated a war to the finish, and even so merely counselled continuing the fight against the Culture after and despite the back-down and attempt to sue for peace which they too believed the Culture must inevitably make.
Having drawn up these «no-lose» formulations of the likely course of events, the Idirans joined battle with the Culture without qualm or hesitation.
At worst, they perhaps considered that the war was being begun in an atmosphere of mutual incomprehension. They could not have envisaged that while they were understood almost too perfectly by their enemy, they had comprehensively misapprehended the forces of belief, need — even fear — and morale operating within the Culture.
The war, briefly (abstract of main text)
The first Idiran-Culture dispute occurred in 1267 AD; the second in 1288; in 1289 the Culture built its first genuine warship for five centuries, in prototype form only (the official excuse was that the generations of Mind-generated warship models the Culture had kept in development had evolved so far from the last warcraft actually built that it was necessary to test the match of theory and practice). In 1307 the third dispute resulted in (machine) fatalities. War was publicly discussed in the Culture as a likelihood for the first time. In 1310 the Peace section of the Culture split from the majority population, while the Anchramin Pit Conference resulted in the agreed withdrawal of forces (a move which the more short-sighted Idirans and Culture citizens respectively condemned and acclaimed).
The fourth dispute began in 1323 and continued (with the Culture using proxy forces) until 1327, when the war officially began and Culture craft and personnel were directly involved. The Culture's War Council of 1326 resulted in several other parts of the Culture splitting away, renouncing the use of violence under any circumstances.
The Idiran-Culture War Conduct Agreement was ratified in 1327. In 1332 the Homomda joined the war on the Idiran side. The Homomda — another tripedal species of greater galactic maturity than either the Culture or the Idirans — had sheltered the Idirans who had made up Holy Remnants during the Second Great Exile (1345-991 BC) following the Skankatrian-Idiran war. The Remnants and their descendants became the Homomdans" most trusted crack ground-troops, and following the Idirans" surprise return and retaking of Idir in 990 BC, the two tripedal species continued to co-operate, on terms that came closer to equality as Idiran power increased.
The Homomda joined with the Idirans because they distrusted the growing power of the Culture (they were far from alone in having this feeling, though unique in acting on it overtly). While having relatively few disagreements with the humans, and none of them serious, it had been Homomdan policy for many tens of thousands of years to attempt to prevent anyone group in the galaxy (on their technological level) from becoming over-strong, a point they decided the Culture was then approaching. The Homomda at no point devoted all their resources to the Idiran cause; they used part of their powerful and efficient space fleet to fill the gaps of quality left in the Idiran navy. It was made clear to the Culture that if the humans attacked Homomdan home planets, only then would the war become total (indeed, limited diplomatic and cultural relations were maintained, and some trade continued, between the Homomda and the Culture throughout the war).
Miscalculations: the Idirans thought they could win alone, and so with Homomdan support assumed they would be invincible; the Homomda thought their influence would tip the balance in the Idirans" favour (though would never have been prepared to risk their own future to defeat the Culture anyway); and the Culture Minds had guessed that the Homomda would not join with the Idirans; calculations concerning the war's duration, cost and benefits had been made on this assumption.
During the war's first phase, the Culture spent most of its time falling back from the rapidly expanding Idiran sphere, completing its war-production change-over and building up its fleet of warships. For those first few years the war in space was effectively fought on the Culture side by its General Contact Units: not designed as warships, but sufficiently well armed and more than fast enough to be a match for the average Idiran ship. In addition, the Culture's field technology had always been ahead of the Idirans', giving the GCUs a decisive advantage in terms of damage avoidance and resistance. These differences to some extent reflected the two sides" general outlooks. To the Idirans a ship was a way of getting from one planet to another, or for defending planets. To the Culture a ship was an exercise in skill, almost a work of art. The GCUs (and the warcraft which gradually replaced them) were created with a combination of enthusiastic flair and machine-orientated practicality the Idirans had no answer to, even if the Culture craft themselves were never quite a match for the better Homomdan ships. For those first years, nevertheless, the GCUs were vastly outnumbered.
That opening stage also saw some of the war's heaviest losses of life, when the Idirans surprise-attacked many war-irrelevant Culture Orbitals, occasionally producing billions of deaths at a time. As a shock tactic this failed. As a military strategy it deflected even more resources from the already stretched Idiran navy's Main Battle Groups, which were experiencing great difficulty in finding and successfully attacking the distant Culture Orbitals, Rocks, factory craft and General Systems Vehicles which were responsible for producing the Culture's materiel. At the same time, the Idirans were attempting to control the vast volumes of space and the large numbers of usually reluctant and often rebellious lesser civilisations the Culture's retreat had left at their mercy. In 1333 the War Conduct Agreement was amended to forbid the destruction of populated, non-military habitats, and the conflict continued in a marginally more restrained fashion until near the end.
The war entered its second phase in 1335. The Idirans were still struggling to consolidate their gains; the Culture was finally on a war footing. A period of protracted struggle ensued as the Culture struck deep into the Idiran sphere, and Idiran policy oscillated between trying to defend what they had and build up their strength, and mounting powerful but defence-weakening expeditions into the rest of the galaxy, attempting to inflict hoped-for body blows upon a foe which proved frustratingly elusive. The Culture was able to use almost the entire galaxy to hide in. Its whole existence was mobile in essence; even Orbitals could be shifted, or simply abandoned, populations moved. The Idirans were religiously committed to taking and holding all they could; to maintaining frontiers, to securing planets and moons; above all, to keeping Idir safe, at any price. Despite Homomdan recommendations, the Idirans refused to fall back to more rational and easily defended volumes, or even to discuss peace.