I recently read JG Ballard's autobiography, Miracles of Life, written in 2008 when he was already dying. The fact that he must have known this lends the book a poignancy, but also a disjointedness - it obviously wasn't in his power to really dedicate himself to realising the project fully. By far the most interesting sections are at the beginning, when Ballard reflects on his time in Shanghai and his famous internment at Lunghua by the Japanese occupying forces between 1942 and 1945. And the most interesting aspect of this story is the brief account of liberation and what followed - the orgy of random violence which the Japanese soldiers inflicted as they vacated Shanghai (he recounts some brutal examples) and the subsequent American takeover of the city.
Ballard asserts, and I have no reason to dispute this, that for months and months (perhaps years) after the end of the war some Japanese troops remained in Shanghai under American leadership, performing guard duties and the like. In the general atmosphere of destruction and chaos, this strange union of former enemies appeared perfectly natural. It reminded me of a film I saw nearly twenty years ago in Japan, called Ari no Heitai or 'Ant Soldiers', which told the story of the Japanese soldiers (some 30,000 of them) who remained in China, after the Second World War had ended, as mercenaries or volunteers fighting for either the Kuomintang or the Communists in the Chinese Civil War.
It also reminded me of the strange fate of the Japanese soldiers captured by Soviet forces in the closing weeks of the war. In Embracing Defeat, John Dower puts the figure of these soldiers at 1.6 million - but nothing like as many were ever repatriated. Some 625,000 were officially returned to Japan by the USSR, and more arrived illegally or unofficially in dribs and drabs after that, but there are still thought to be anywhere between 250,000 and 500,000 who are unaccounted for. Presumably some of these will have died or ended up in gulags, but occasionally on Japanese TV documentaries will be aired about the discovery of the descendants of such soldiers in the far-flung corners of Siberia.
Widening the focus, there is of course the famous story of the Czechoslovak Legion, a unit of the Imperial Russian Army comprising Czech and Slovak volunteers, who found themselves stranded in Russia in 1918 when the Bolsheviks, having recently seized power, negotiated the Treaty of Brest-Litovsk with Germany and ended the war. The Legion, its members desiring to travel to the Western Front to continue fighting the Central Powers, but unable to get there directly by land travelling westwards, decided to go eastwards instead and go all the way to Vladivostok, then catch a boat to France. They then became embroiled in the Russian Civil War on the side of the Whites, and at one point even participated in the seizure of the old Russian Imperial gold reserve.
And widening it yet further to fiction, there are a few examples of books and films taking place in the immediate, and still often violent and chaotic, aftermath of a war. Gene Wolfe's Soldier of the Mist series is one of my favourite examples - the action takes place shortly after the climax of the failed invasion of Greece by Persia at Plataea in 479 BC, and the main character, Latro, it is assumed sustained his amnesia-inducing head injury during that battle. The detritus of war, and the confusion, with vast numbers of people (civilians and soldiers alike) going this way and that in search of home, whether the old home or a new one, is nicely described by Wolfe in that novel. A leftfield choice, but a very enjoyable flick, is Three Kings, in which three bored US soldiers with nothing to do at the end of the first Gulf War decide to go off on a heist and become embroiled in the general chaos and mayhem of post-war Iraq. You could probably also put Cold Mountain in this category; while I'm not sure whether the events depicted in it happen before or after the US Civil War ended, the depiction of a wandering soldier making his way home across a landscape torn and destabilised by conflict is truly compelling.
The beauty of the War Aftermath campaign mode is that it creates a landscape within which adventure and derring-do are pretty much assumed, but also that it creates the space within which a very wide breadth of choice opens up in respect of play style. The PCs might be purely self-interested rogues wandering here and there looting treasure. But they might equally be self-conscious 'good guys' trying to help the weak and unfortunate - or anything in between.
And the generalised atmosphere of chaos and confusion can be highly conducive to creative DMing. Imagine a bucolic fantasy landscape such as the Shire in the aftermath of an invasion by an army of interlopers from the Abyss and the subsequent vanquishing of said Abyssal horde by an army of quasi-angelic high elves. What strange beings would be hidden in that landscape, wounded or hidden? What might have been left behind by way of loot by the retreating army? What wandering mercenaries, bands of prisoners and their guards, messengers and refugees would be coming and going, hurrying along or tarrying, behind the next hill or forest? What opportunities would like in store for a band of ex-soldiers now foot loose and fancy free? What would befall a group of ordinary peasants searching for a lost home or family?