The rather different explanation you give for the German loss of Poznan and Alsace-Lorraine than before (simply due to socialist regard for self-determination) is much more palatable to me (and Dachs, I suppose, although he won't like the result), although the vastly different implications it has for irredentist movements do seem to put this Spartakist Germany (love the name, by the way) into more of a Third Reich analogue.
Nah, it was actually a bit of both - Lorraine-Alsace and Poznan were self-determination, but France and Poland tried to push their claims further, claiming the Ruhr and the Danzig Corridor respectively, and subsequently were repulsed. There was some talk in the Reichstag of taking it further, but both out of principle and due to pragmatic considerations that was where it ended. There isn't actually all that much of an irredentist movement in Germany; foreign policy is more a blend of socialist internationalism and statist pragmatism, which, ofcourse, still makes reclaiming Poznan and Lorraine-Alsace look enticing.
How has the French economy done after the rise of the integralists?
Not bad, actually; while commerce has suffered somewhat from excessive protectionism and industrial development was perhaps too heavily tilted towards military needs, the overall state of economy is actually markedly better than in OTL - much less unemployment, substantial development of industry and particularly infrastructure, and finance isn't nearly as big a mess for a variety of reasons. A degree of economic dirigisme has generally helped things, as had the loss of numerous cumbersome colonies. The impetus of economic development might run out in the near future, though.
Did the civil wars in Germany help turn the demographic tide any in regards to population disparity?
Not really; after the war the French were struggling in the demographics department even more so than in OTL, and the subsequent attempts of the new government to rectify this situation have been a limited success so far. This might change in the future as time goes, or it might not if the positive economic trends do not keep up.
Is France still widely regarded as the strongest European army on paper, or has someone else ceased that mantle?
There isn't really any nation that could claim to have the strongest army in Europe. The French lost the war, remember? And then they lost
another war, to the same Germans that supposedly were defeated. Germany held the reputation of being the strongest in Europe for quite a while, but then the 1931 war with Poland happened and that has dispelled any illusions. The French army right now is almost definitely stronger than the OTL one, being much more eager to embrace new doctrines and technologies, and the Germans have been rapidly catching up since, though they are actually more conservative in their doctrine than in OTL. Poland would be a serious contender if people had gotten used to taking it seriously, which they haven't, and its army isn't all that large. The new and improved Russian army is pretty solid in its own way - what it lacks in tanks it makes up for in its air force, and its officer corps is elite - but it hasn't been proven in battle against foreign powers, and its rather smaller than what a lot of people might expect. Britain hasn't neglected its army nearly as much as in OTL interwar period, but still, its Britain.
When you say the great depression was 'weaker' but then make comments about the entire structural problems of the British Empire, did the epicenter of the financial collapse happen in Britain and not America, then?
No, it was still in America, but Britain had even more of its own problems than in OTL, and so was affected more strongly than in OTL. Having become increasingly reliant on the US due to the chaos in Europe didn't help, either. They're trying to fix this now, by reviving the ghost of Joseph Chamberlain among other things; it's not really working yet.
At what specific points are the British Empire crumbling under its own weight? Have the various Indian independence movements gained any more traction than they have OTL?
Ireland, India, the Middle East, former French colonies. The Indian National Congress has actually been courted as a major ally with promises of further Imperial reform with regards to India in particular, though there certainly is a fairly strong anti-British, independence-now undercurrent; but if anything, it is actually weaker than in OTL. It's not as good elsewhere - Ireland is a horrible quagmire (I mean, even more so than usual), the Arab nationalists are really acting up and control over former French West Africa is slipping (an overwhelming amount of the French colonists have left since the late 1920s, crippling local administration, and the local elites are being antagonistic). Mostly its overall overstretch, and, ofcourse, the loss of economic positions.
How icy are diplomatic relations between the various Eastern European military dictatorships, and for that matter, Italy and Greece?
Pretty icy, really. Hungary wants to take over the whole of Croatia, and so does Serbia. Serbs and Greeks alike want Albania (though they are actually likely to work out an alliance on this basis). Turks hate everyone (but are willing to play them off against each other). Bulgaria is an Agrarian Socialist-dominated republic which still wants to take over the whole of Macedonia.
If the radical communists in China are insurgencies, what is the Xinjiang (Uyghurstan?) and Gansu based states there?
Warlord cliques. Tribal Turkmen- and Muslim Chinese-flavoured, respectively. The former are leery of Turan, the latter are actually quite cooperative towards both Turan and the Communist insurrectionists, no doubt out of sheer pragmatism.
Of the Far Eastern Siberian republics, which is the American and which is the Japanese puppet?
North is American; pretends to be a republic - badly, though it actually has been something of a haven for those of the Russian Social-Democrats that are neither dead nor in Europe. Still, dominant elements are a local Russian army clique with highly-tenuous connections to the White Guard movement and much more prominent connections to American military advisers. South is Japanese, and it's much more respectable, drawing in part on pre-war local administrative and military circles and, ofcourse, being controlled fairly closely by agents of the Kwantung Army, who are (reputedly) entertaining the idea of creating the Army's Navy there (ofcourse!).
Does the Beijing military government fall along the lines of the Wang Jingwei puppet state established in OTL WWII, or does it have greater autonomy than that?
Oh I should say so! It's the remains of the Beiyang Clique. They have their own established power-base, but are willing to make concessions to the Japanese in exchange for first fending off and then pushing back the damned Southerners, and to work together with Japanese Army structures (while also trying to play the Navy off against it).
How the hell did the American politicians convince the American public that a more ambitious Japan was sufficient cause for breaking its tradition of isolationism, especially the complete (even moreso than OTL) failure of America interventionism in WWI?
America had to some extent "turned away" from Europe after the war and its aftermath, and this resulted in a partial shift of focus towards the Pacific and particularly China, where the Republic was viewed with quite some hope. The alarming growth of Japanese economic, political and military presence had first alarmed the political and military leadership, then the business circles, then finally the greater public; the latter was a gradual and uneven process, but it has happened nonetheless to such an extent that it has become a public sentiment that a stance must be taken against some particularly exceptional cases of Japanese pushiness (but not yet to the extent of actually going to war!). Even earlier, the general support of financial and political elites was enough to provide some limited assistance to Japan's opponents. Note, though, that public opinion was isolationist enough to allow the Japanese to establish themselves in both the Russian Far East and the French Indochina, despite all the outbursts of panic that has caused in the right circles; it was only afterwards that public opinion began to flip out over what has apparently been allowed.
Have there been any major population transfers a la the OTL Treaty of Lausanne or the entirety of Poland moving west after WWII?
Not as such. Well, there have been efforts to push out the Turks from the lands they had lost, especially by Greeks, but those were only partially successful for now. The late 1920s-early 1930s French exodus from their lost colonies might count, but note that it's not a very large population to begin with.
Transylvania must be returned to her rightful Magyar lords, then.
Well, about a half of it anyway.
So, did all the Romanovs and their main noble cronies get offed, or exiled, or what?
Well, the October Revolution still happened, and the Romanov main line was still imprisoned and ultimately executed, though in this case it was perceived as more of an act of desperation. The Bolsheviks were defeated as war moved into Russia: Germans tried to impose their puppet government, while the Anglo-Americans backed the pro-Entente White Guard mainstream; then when everything collapsed there was a relatively brief period of warlordism in European Russia that ended when one of the military factions managed to unite the others and beat up those who didn't agree as well as any remaining Red or Green forces. They couldn't agree on anything like a restoration, though, as the dynastic affairs had become terribly muddled by then and many of the officers turned out to be actually in favour of a "national" republic; so the remaining Romanovs are still languishing in exile despite occasional talk of a restoration in Muscovite political circles, and the same goes for a fair amount of aristocrats. Other aristocrats remained and continue to play prominent parts in government and industry, but titles are, by this point, purely cosmetic; the post-war Russian political elite is more informal and determined by connections to the military-industrial complex and/or the officer societies.