Intentions and grand strategy are one thing, but as a conflict heats up and becomes more desperate, those things begin to disappear. Time and time again we see powers enter into a conflict with their chosen battery of doctrines and tactics, only to have those blueprints go up in flames as the powers bog down and the fighting becomes prolonged and tortured. The heat makes malleable what was assumed to be rigid and immutable; the chaos sets in, and the unforeseen consequences begin to crop up, or else seeds are sown whose fruit may not be known for another century or more, after which the lessons are forgotten anyway.
What is required for things to get really hot? The conditions can be quite variable, and thus unpredictable. Different geographies and environments alter the terrain for what constitutes sound tactics and technologies. What is at stake? What does a given power want? And generally the more powers entering, the more materials and abilities involved, the more prolonged the conflict becomes, and the greater the scope of the conflict, threatening to subsume more concerns and interests for further removed powers.
As with revolution and civil war, we see profound changes happen in a society too: power may be centralized and consolidated somewhere where it is dispersed and scattered elsewhere, such as in the nationalization of industry, and social and cultural roles and mores may be stretched or even transformed. Weak empires may be broken, ascendant empires may be made, and international relations may shift. In desperate times, the changes needed for national survival may be instituted as a matter of necessity, where the dithering with gaslighting and PR and interest group veto may no longer be afforded.
