Inspired by the Ribbentrop Beck Pact, i started to wonder ... what if Stalin, for whatever reason, declines to invade Poland as planned in 1939?
Chris
OK. Perhaps Stalin has signed the pact and taken OTL's actions up to this point, because he expects the Anglo-French are bluffing and will settle with Germany and not really declare war. So, his agreement to the Molotov-Ribbentropp pact and trade agreements are a necessary, provisional hedge to keep peace on his western border and protect it in case Germany ends up unencumbered by war in the west.
I can provide a "Why"
In OTL, Stalin stuck with the M-R pact even after Britain and France declared war on Germany for multiple reasons: a) really wanted the agreed territorial concessions, b) it soon became apparent the western allies were not fighting vigorously on the land or the air, c) he wanted the military-industrial tech imports from Germany as part of the deal.
In this ATL, the fact that Britain and France actually declare war on Germany, that they ruthlessly prosecute economic warfare, including blockade, and that the French even make moves in the Saar is a pleasant surprise to Stalin. It impresses him enough that he decides he does not want to impede Allied anti-German efforts in any way or facilitate German military success in any way.
So, September 17th comes and goes, and the Soviet Union does not move across the Polish border.
Nazi operations pursuing the Poles continue into the erstwhile Soviet occupation zone, generally succeeding against the Poles, but using up more men, fuel, vehicles and horses as they continue. They become a little more tricky as they reach the swampier, Belarussian areas of northeast Poland, with many Polish soldiers able to disperse as partisans. The Lithuanians, with positive German encouragement, and reluctant Soviet acquiescence, occupy the greater Vilnius region.
The greater share of surviving Polish forces are still fighting and being pursued in southeastern Poland, south of the Pripet marshes, seeking to hold open lines of communication to Romania at all costs.
By the end of September, the Germans are getting irritated with the Soviets and asking them to clarify whether they are intending on respecting the nonaggression pact, the secret territorial clauses, and the trade deals, and when. The Soviets reply they intend absolutely to adhere to all agreements, yield none of their territorial rights over the long-term, and reserve for themselves the right to determine the soonest practical time to actualize the terms of the agreement and collect what is theirs.
In line with their passive, wait behind their borders posture, the Soviets continue to build up their forces in their western military districts and build-up the Stalin Line. Since they have avoided the opprobrium of invading Poland, they also avoid invading Finland and the Baltics.
Wherever Polish forces get forced by German pursuit across the Soviet border, the Soviets intern them. The Soviets sort them by ethnicity, retaining and reeducating ethnic Belarussian and Ukrainians for their own later purposes and eliminating any deemed unreliable, and sending ethnic Poles on to join Polish compatriots in Romania.
As 1939 turns to winter, all Poland is occupied by Germany (or Lithuania), despite the continued existence of partisans) except for the few Carpathian foothills districts of the "Romanian bridgehead" that the Wehrmacht and Luftwaffe have under siege. Luftwaffe bombing has extended to adjoining areas across the Romanian border.
The Germans approach the new year 1940 with competing imperatives- needing to strike west to at least expand their siege lines for operations against Britain and France, and hopefully to crush France, needing to strike southeast to crush the remnant Poles and secure the Romanian oil supply, needing to secure the Scandinavian iron ore supply to the north.
The French and British continue to mobilize their force in the west. The British Admiralty seeks to tighten the blockade, including by mining Norwegian fjords. The French in particular are keen to keep delaying main action in the west to permit the growth of BEF forces joining them, and see the survival of remnant Poles, and Romanian cooperation with those forces, as a great asset to be used to tie down the Germans as long as possible. Therefore, the British and French send the aid they can to the Romanians and remnant Poles.
The Soviets are trading with the Germans, but are always trying to front load incoming cargoes and slow down outgoing cargo deliveries.
They still swear by the non-aggression pact however.
Hitler reluctantly concludes early in 1940 that a preliminary campaign to crush the Romanian bridgehead, and Romania in early spring 1940 is vital before turning west for a summer 1940 offensive in the west.
This is to prevent any surprises in the east and secure a diverse oil supply. He also considers the necessity of a northern preliminary operation to seize Denmark and Norway to secure Swedish ore, but this may not be quite as urgent in this ATL without the Finland war diverting attention in that direction.
Hitler masses the forces that crushed Poland in southeast Poland, Slovakia, and Hungary in time for the spring 1940 thaw, and from early April launches a multi-Axis assault into Transylvania, Oltenia, and Moldavia, aimed at the total destruction of the Romania armed forces, the total occupation of its territory down to the Danube river and the destruction of the Polish refugee forces and redoubt. Slovakia, and particularly Hungary are enthusiastic allies in this campaign, and Bulgaria joins in for the spoils of northern Dobruja. The Axis powers occupy Ploesti, but temporarily lose considerable fuel production to sabotage that they have to repair.
Ultimately, the Germans occupy Romania up to its border with the Soviet Union on the Dniester river, despite prior acknowledgement of Bessarabia being in the Soviet sphere of influence.
Within a week or two after the "Danubian" operation starting, the Germans invade Denmark and then Norway in a daring seaborne and airborne operation.
This is likely to succeed in its southern and central sectors, with a greater chance of failure in its northern sector.
The scale of these operations takes time for completion, rest, refit, and redeployment.
The German forces open their offensive in the west against the Low Countries and France in late June 1940. Some of the newer American aircraft are by this point in service with the French Air Force, and more BEF units are in place.
As a result of the later start in the west, greater Allied build-up, and greater wear and tear on German forces from more protracted and continuous campaigning, the Germans are halted in Belgium and northern France.
The mid-campaign stalemate in Belgium also prevents Germany from turning the stalemate in Norway, north of Narvik, in its favor.
The Soviet Union takes advantage of Germany's battlefield setback and need for a greater trickle of supplies by August 1940 to demand the handover of the eastern Polish and Romanian territories it is owed by Germany. Since Bukovina was not covered under the agreements, the USSR gets no territory there.
From the onset of the late summer 1940 stalemate onwards, the combat skill levels of the western Allies and Germans gradually begin to equalize.
The Soviets incorporate and reinforce their newly occupied territories in former eastern Poland and Bessarabia.
With the survival of France, with its metropolitan territory even more intact than in WWI, Italy does not declare war against the Allies. Japan also remains relatively cautious, not occupying French Indochina.
German attempts to break the western stalemate in the fall of 1940 and in 1941 fail, but flexible and tenacious German defenses also thwart western attempts to break the stalemate from their direction. German forces are significantly attrited and demotorized with greater emphasis on animal power by the end of 1941 compared with the beginning of 1941 however, and air superiority has shifted in the Allies direction.
The Soviets barely hold up their end of the Nazi-Soviet trade bargain, keeping Germany supplied with a bare minimum needed supply of POL and food in exchange for military designs.
The Germans conscript wide manpower classes and allied manpower from Hungary and Slovakia, and Kresy Ukrainians they hired into service in their occupation period there to keep up their manpower numbers. The Western Allies keep up their manpower numbers with mobilization of metropolitan manpower, and increases levies by France from its colonial possessions and increased British employment of Dominion units and larger numbers of American volunteers.
As 1941 turns to 1942, the Soviets feel ready to intervene, using the seasons to their advantage. They stall on deliveries to Germany from January 1942, and launch a late winter assault from February 15th, to seize central and southern Poland and eastern Romania to gain control of Warsaw, Lodz, and Bucharest and crush Axis forward forces and fortifications.
Despite shortfalls in tactical and operational performance, the Soviets meet their territorial goals, wound Axis forces, especially Hungarian and Slovak ones, and seize the erstwhile Polish and Romanian capitals. They also have Ploesti in easy bombing range and long-range artillery range. Also, Soviet initial success in Central Poland is enough to convince Lithuania to succumb to the Soviet ultimatum to let Soviet forces pass through Lithuania to attack East Prussia, in return for Lithuania winning back Memel.
The Soviet surprise attack forces Axis redeployments from the western front and enables Allied advances in Belgium and the fringes of the Netherlands and Rhineland.
The seasonal factor also limits the scope of the possible German counterattack against Soviet forces after those forces reach their culminating point. This is because just as the Germans are capable of massing truly large concentrations of armor, artillery, and air power in the east to execute large and deep encirclements of the Soviet invaders, the March and April rains have begun turning the ground in Central Europe muddy and clouded up the clear flying weather.
Man for man and unit for unit, the German air and ground units are outperforming the Soviets. When the weather clears and ground dries, they are poised to become more dangerous to forward Soviet forces. But the Soviets are putting the rain and mud season to great use bringing up resupply and bringing up the next echelons of forces, while also beginning to raise up loyal Romanian and Polish and (mostly Slovak) Czechoslovakian formations from the liberated population.