Here's an idea:
Polish cryptographers break Soviet codes much earlier in the Polish-Soviet War of the early 1920s. Consequently, Poland makes it to Kiev and Minsk, holding a vague front from the Dnieper to the Pripiat marshes.
Soviet defeats encourage Finland in their (in OTL utterly failed) expedition to liberate Karelia and their co-ethnics from the Bolsheviks. ITTL, the expedition succeeds. Polish and Finnish successes, along with the continued existence of a White Army in the Crimea, and prolonged Japanese occupation of the Russian Far East cause the Soviet leadership to agree to terms with Helsinki and Warsaw.
The Polish government after the peace is dominated by "Big Poland" advocates of Inter-Marum alliance or federation. It manages to establish an officially federative state with (western) Ukraine and Belarus; which retains difficulties (like Lwow/Lviv) but is workable, especially after the Soviet invasion of the last remaining outpost of White Russian forces on the Crimean Peninsula drives home fears of a communist resurgence.
As a side effect of the different Polish-Soviet war, Czechoslovakia and Poland are able to arrive at a French-mediated agreement on border disputes. Neither is completely happy with the agreement, but in the background of Polish commitments elsewhere, Warsaw manages to accept.
Meanwhile in the 1920s, France works with the new states of Central Europe and the Balkans. The Little Entente is formed, initially to prevent a Hapsburg restoration in Hungary or Austria. By 1929, Czechoslovakia drops its "concerns" over Polish entry into the alliance, which is complete by 1931.
The Great Depression wracks the world economy in the early 1930s, and the Nazis come to power in Germany. Under Mussolini, Italy rearms and increases its indirect control in Albania.
When Germany absorbs Austria in 1936, the Italian position has become much more obviously pro-Berlin. With active solicitation and lobbying by Yugoslavia, Greece joins the Inter-Marum alliance, or the Little Entente.
A rapidly arming and increasingly aggressive Germany begins to make demands on Czechoslovakia over the Sudetenland. Prague rejects them, counting particularly on French guarantees to stay the German hand. Unfortunately, the initial responses from Paris and London are muddled, with noises of appeasement. Hitler takes this as a sign the western democracies will not intervene, war begins after a German ultimatum.
France does not initially declare war, but begins to mobilize. Prague's other allies have already done so along with Czechoslovakia, and do declare war after the German ultimatum rejects their diplomatic assurances of support for the country.
The initial phase of the war sees slow, grinding combat in the hills and mountains of the Sudetenland. Skirmishing also occurs on the border between Yugoslavia and Austria, but the terrain there precludes an advance with what either side has available. The Poles begin their invasions of East Prussia and German Silesia at this time as well. Unfortunately for them, the unmechanized nature of the Polish army, and the preparations of the Germans prevents a major breakout. Nevertheless, Germany is denied the quick victory it needs. Losses in men and material must be carefully minimized in order to maintain some ability to respond in the event France finally intervenes.
France does precisely this once the humiliation of ignoring a pledge of support to "the valiant Czechs" sinks in. With a declaration of war, France and Germany begin trading air raids, and French aid begins to flow to her eastern allies. Paris is still quite cautious over an invasion into the Rhineland, but the outbreak of war with France causes near-panic in the Wehrmacht. Many doubt that German defenses could hold a full-scale French invasion, especially while combat in the east continues.
The first careful French probes into the German lines are astonished to find such a poor state of the opposing forces. Political questions of cowardice or incompetence are quietly raised among French leadership. Added to the relentless pressure from Warsaw and Prague for action, the French army prepares to co-ordinate a full offensive.
The incomplete German Westwall collapses against the French tide. On the eastern front, Polish forces begin to make quick progress in rolling up Silesia, while the Czechoslovakians manage to push the Germans back from many of their gains.
The German army sees the writing on the wall, and attempts a coup. Unfortunately, the plotters are discovered and the coup d'etat is only partially successful. Hitler is killed, but many of the officers involved are either shot or arrested. Amid the chaos in German high command, France seizes Mainz, and the Poles have cut the remaining German forces in Silesia off from Germany. Feuding leadership in the post-coup environment in Berlin descends into anarchy, leaving little coherent government in much of Germany, much less the front.
German forces surrender en masse, particularly on the orders of their local commanders. In Berlin, army units loyal to the coup leaders take control, and the country officially requests an armistice.
Terms on the defeated Germany are not quite as harsh as they could have been, but are highly visible. East Prussia is reduced to a militarily insignificant enclave around Koningsburg. Silesia is greatly reduced, as the entirety of Polish demands after the First World War are fulfilled. Danzig and a slice of eastern Pomerania fall under Polish control. Austria regains its independence.
Czechoslovakia and France are also given various compensations, and allied forces occupy strategic points in Germany to oversee a full disarmament. In particular, France returns to occupation of the Rhineland.
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How's that work out for all of you?