Making Chinese geopolitics interesting...in the Chinese sense.
Officially Paritioning China is something that not even Victorian Europe tried at the height of its power and the nadir of Chinese ability to resist European and American dominance. Forcibly taking northern china and making it independent of the more populous regions to the south is going to go over like a lead balloon at the peace-talks; especially since I'd presume that the Comintern would not recognize Japan's occupation of inner Mongolia and Manchuria as actually being legitimate. And while places like Xinjiang were de facto independent and under heavy soviet influence, de jure they are still part of China and Jingwei's going to react to Soviet attempts at kicking china out of central asia really poorly; particularly with Tibet already being under the Alliance of Free States and thus already taking a chunk out of Central Asia from China.
I think it can be done if we consider certain factors and butterflies ITTL. IOTL the Chinese government largely abandoned the north to brutal Japanese occupation, to focus on defending the south and coastal regions. This enabled the CPC, allied with the government but still very much independent from it, to gain a lot of good will from the local population when they liberated it from the Japanese and resisted them, whilst also destroying the image of the KMT in those regions. ITTL, however, the CPC and KMT are allied and cooperating on a far greater level, maybe to the extent that the CPC's armed forces are integrated into the Chinese army. As a result, when the KMT decides to abandon the north for the south, the CPC follow with them, or at least leaves fewer soldiers behind to resist the Japanese. This means that both the KMT and CPC lose support in the north, and it’s the Soviet and Mongolian armed forces that expel the Japanese from Inner Mongolia, rather than the Chinese. Furthermore, because of less resistance in the north, the Japanese are able to penetrate even further, which spooks the government in Xinjiang, and causes them to build even closer ties with the Soviets for protection, eventually petitioning the Soviet Union to join as an SSR.
Another thing to consider is that IOTL Marshal Khorloogiin Choibalsan, the socialist leader of Mongolia, was a big supporter of pan-Mongolian nationalism, and wanted Mongolia to be united under his rule, but Stalin kept torpedoing his moves towards it. I believe at one point he suggested that there should be a referendum in Inner Mongolia after the Communists won, but Stalin shot that suggestion down. ITTL, I believe Stalin dies earlier, and in any case the Soviet Union is going to be weary of losing influence in the far-East to the Americans, so they decide to go along with it and don't block his attempts to encourage pan-Mongolism. The USAR agrees to back a referendum because democracy and national self-determination FTW, and under pressure Jingwei reluctantly agrees to it, and it all goes downhill from there.
A rough outline of events might look something like this:
Shortly before the war ends, Xinjiang joins the Soviet Union as the East Turkestan SSR. The remnants of the KMT right are livid, and there are some grumblings from the KMT left, whilst the CPC is generally supportive. Jingwei reluctantly allows this to happen, after all Xinjiang is a peripheral territory, that's mostly desert, and the locals are more Turkic than Chinese anyway. Beside, we're all comrades now, he still need to focus on defeating the Japanese, and he'll probably be able to get it back diplomatically later.
After the war ends, the SU pushes for a referendum in Inner Mongolia, and under external pressure from the USAR and internal pressure from the CPC, Jingwei reluctantly agrees. What's the worst that could happen?
Chinese Mongols vote in favour of unification. Jingwei is now under heavy fire from both the right and the left of the KMT, and even the CPC are starting to realise that they may have miscalculated with supporting the referendum.
The right and moderate left of the KMT begin to form an anti-Comintern faction. Whilst ostensibly still in favour of socialism, they feel that continued membership of the Comintern would mean sacrificing China's interests to foreign powers. Furthermore, there's a lot of resentment within the KMT towards the CPC that's been building up for some time now, with many seeing them as having undue influence due to foreign interference, and being willing to sacrifice Chinese interests in the name of Communism.
The SU, wanting to see how far they can push things decide to call for a referendum in Manchuria, but this is the last straw. Anti-Comintern officers attempt to stage a coup in Nanjing, hoping to destroy the CPC and force Jingwei to stand down in favour of a more centrist candidate. Things don't go as planned, however, and the coup fails, although not before Mao is killed.
News of the attempted coup triggers a wave of violence across the country with red and white terror running rampant. The military, warlords, and local governments find themselves forced to pick sides, and the country descends into civil war. As the war drags on the left-wing elements of the rebels are sidelined, and it becomes steadily more anti-Communist, drawing more and more reactionary elements to its banner, ranging from liberals and the KMT right to fascists and monarchists. At the same time, the pro-government forces become more radical, with the CPC seeing the civil war as an opportunity to implement a second stage revolution, and purge the remaining bourgeois elements. As the fighting gets more intense, Tibet declares independence from China.
The Soviets, having thoroughly burnt their bridges with the Chinese at this point, send troops to help "secure" Manchuria. The Soviet troops "oversee" a referendum on Manchurian independence, which votes 80% in favour of independence. The Chinese and American's don't believe the referendum for a second, but the Soviets are there, they have nukes, and they have bigger fish to fry. The Soviets, more keen to consolidate their hold over northern China, decide to not get involved with the civil war, and forbid their satellites from getting involved. This does not go down well with the USAR, and the growing split between them grows.
The USAR fully commits to supporting the government in the civil war, and supplies them with material and soldiers.
The Korean poliburo, split between pro-American and pro-Soviet factions agree on a compromise, sending material and volunteers under the command of the anarchists (possibly Park Yeol, but if Kim Jwa-jin's assassination can be butterflied away, then things would get interesting). This way they can support the cause and keep both the Americans and Soviets happy, whilst also getting rid of the anarchist gadflies who can go get themselves killed fighting the whites (which couldn't possibly backfire).
The newly established Japanese Republic also declares for the government and sends troops, however they are limited in what they can do, given that most of the old army officers are either dead, in jail, or have gone underground to fight a guerilla insurgency against the new government, which much of their current military is trying to put down. In the end it is decided to release some of the officers and place them under guard, and a small expeditionary force is sent, with the intention being that they will serve as a garrison force, allowing the government to free up forces to crush the rebel scum. This is not a popular move with the wider Japanese population, with many seeing it as plunging Japan into another brutal and costly war, and is complicated when large numbers of the expeditionary forced begin to mutiny and defect to the White Chinese. To add further confusion into the mix, the Japanese anarchist movement begin organising a volunteer force that joins up with the Korean volunteers. The JCP, not without justification, sees this as an attempt by the anarchists to undermine their authority, and this contributes to the eventual expulsion of the Anarcho-Syndicalists from the JCP.
The nascent FBU, still under a Labour/Socialist government, initially supports a peaceful and diplomatic solution to the war, but refuses to get sucked into the violence. Their local colonial governments, on the other hand, seem to be lacking in such noble sentiments, and covertly support the whites, sending material and offering their troops safe haven, whilst many of the POW camps holding Japanese soldiers, suddenly seem to have fewer prisoners. Things really start to change after the FBU election, when the Labour/Socialist government is ousted by the Churchillites/Gaulites who throw their support behind the whites. The Soviet Union still refuses to get involved, but the USAR sends an ultimatum to London, demanding that they back down or the USAR will declare war on the FBU. The FBU calls that American's bluff and refuses to back down, the Americans blink and agree to a ceasefire, and World War 3 is narrowly avoided. At this point the Whites, who were being pushed back and were dependent on support coming through Hong Kong and Indochina, are concentrated in Liangguangin, controlling of most of Guangxi and Guangdong, as well as all of Haina and bits of Jiangxi and Fujia. Tibet becomes a protectorate of the FBU, but it is left ambiguous as to whether they view it as a separate entity, or an autonomous part of China.
Jingwei decides it's best to retire from politics.
During the 50s and 60s the White Chinese regime, initially a military dictatorship, undergoes a period of liberalisation under pressure from the FBU, renouncing their claim to all of China and embracing a Cantonese/Hakka nationalist ideology in order to build local support and legitimacy for the regime, which also allows the FBU to integrate Tibet into India to appease and co-opt pan-Indian sentiment. During the 70s, however, things start to go downhill following the fall of Indochina, reconciliation between the USAR and Soviet Union, and the Canada Crisis, and the Cantonese Republic takes a hard-right turn and a return to military rule. Whilst not North Korea levels of tyranny, it’s not a very nice place. Eventually Macau and Hong Kong are “returned” to Canton, which pisses the Chinese off to no end.
The long-term effects of the civil war on the RoC are extensive. Firstly, the KMT lose a lot of power and influence in the short term, following the purge of the anti-Comintern bloc, which created a power vacuum that is filled by the CPC and the rising anarchist movement, which had gained a boost from the aforementioned Korean and Japanese anarchist volunteers, as well as some of the USAR’s soldiers. This would form the basis of China’s tri-partite system. Secondly, as a result of the succession crisis, China would take a very hard nationalist line on domestic and cultural policy, favouring strong assimilationist policies (in the name of building a “proletarian culture”) and viewing minorities as potential fifth columnists (which in turn inspired the sort of policies that turned that into a self-fulfilling prophecy, such as banning Cantonese in schools). Although this stance would soften following the reconciliation of the USSR and USAR in the 70s, during which China renounced their claims on East Turkestan and recognised the Mongolian and Manchurian governments, the Chinese government is still firmly committed to Chinese reunification, albeit through diplomatic means where Manchuria and Mongolia are concerned.
The civil war is also largely responsible for shaping Soviet and American foreign policy in Asia, with the Soviets tending to back separatist movements in the FBU sphere and condemning “Han social chauvinism” in China with regards to Taiwan and Yunnan, whilst the USAR favoured pan-nationalist movements, particularly pan-Chinese and pan-Indian (sans Tibet which they regard as being rightfully Chinese) movements. This had the unfortunate effect of splitting the revolutionary left, particularly in India, helping to stabilise FBU rule in the immediate post-war period.
One peculiarity of Chinese geopolitics is that in the FBU Chinese food tends to be associated with Cantonese cuisine, whilst in the USAR it tends to be associated with Szechuan cuisine. This has led to more than amusing incident involving Franco-British tourists in the USAR unaware of this little fact.
