You seem to think this shocking scenario, but I am not sure why. You need to provide more details.
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Also, I am not arguing "wise", I am stating the most likely course of action for the Tsar's army. We know the War Plan, and normally countries execute some variation of the War Plan in the first days/months of the war.
OTL, Plan No. 19 in 1910 changed the whole Russian war plan and broke with the defensive tradition. I argue that the French knowledge of the Schlieffen plan is only one factor in this decision. Between 1905 and 1914, Russian strength grew far more rapidly than Germany's, "artificially" due to recovery from the desaster of 1904/05, but also due to a solid economical growth which allowed to keep pace in the European arms race. Along with that grew the necessity not to give up important economically strong areas. 1914 is different from 1812 as well as 1941...giving way would be a dangerous game.
The French presentation of Plan XVI acknowledged the positive Russian development: « L’entente cordiale donne à la France toute sécurité sur son front de mer ; elle lui fait même espérer l’appui de forces militaires anglaises. La mobilisation et la concentration russes ont été sensiblement améliorées »
Furthermore I argue that the lack of the Schlieffen-plan increases the need for a Russian offensive, as British involvement with all its beneficial factors remains much more of an incertainty. With the UK in the war (and the ensuing blockade), Entente planners could (to a good degree justifiably so) predict that economic pressure would weaken the CP over time decisively so that victory was certain. Without it, there is more need to apply the advantages of being on the outer rim of a two front war plus enjoying numerical superiority. This is NOT relaxing one front in order to allow the "central party" to shuffle its troops according to its needs, but to apply pressure on as many points as possible. This is what the Entente IOTL tried in 1914 as well as in 1916.
I do not argue that Russia would ITTL go to war with exactly the same plan as in OTL. Not every plan is as fixed as the German folly called "Schlieffen-plan", anyways. Even the much deriled French plan XVII was actually not much more than a mobilisation scheme which left it to the executing generals what to do with it. Despite being confronted with the bulk of the German army (and knowing it), they decided to stage a massive attack instead of letting Russia decide the war.
I also do not argue that Russia couldn't act flexibly on the Westernmost Polish border. It actually would give them the freedom to concentrate on the flanks: attacking East Prussia would shorten the front in a more positive way, and pushing against Austria-Hungary would give the chance to cripple the weaker partner of the Central Powers while liberating unhappy Ruthenes and Ukrainians.
IOTL, the Battles in the west became bloody and indecisive by 1/1/1915. ITTL, the French will have indecisive battles a few weeks to a couple months earlier, so I guess it would move up French innovation by few months, maybe. You likely have some bloody Verdun/Somme like battles in 1915 and 1916 by the French.
75,000 dead Poilus during the very first month of war, to a good deal during the bloody and indecisive attack against Alsace-Lorraine, was a good foretaste IOTL. They'll learn faster, though, because there will be no "miracle on the Marne" giving 1914 a positive outlook.
I'd say that considering the often hilly terrain, Verdun will be a good analogy to what is to be expected on that frontier.
UK will eventually try to enter the war or otherwise keep Germany from dominating Europe, but not on the first days of the war. Germany also has more material early in the war.
I think that is one of the decisive "if"'s. My hope would be that British neutrality keeps the Germans away from demanding to much in exchange for peace. Then Britain could broker peace, safe the Tsar and get out of the bloodbath unscathed. There is also the possibility that if news of the attrition battles reach the British public relatively uncensored, there might be a surge of sudden "really splendid isolation"ism.
The later Britain enters, the larger the advantage for the Germans. Every month of unhindered access to the global markets is worth millions and millions for the German war effort. How fast would British mobilization be under the changed circumstances? How long would it take until they have reached the effecivity they displayed in the 2nd half of the war?
An interesting point to discuss is the effect on the US. If they do not stick to neutrality completey (without Belgian atrocities, with a later U-Boot-war, with a more balanced economical interest), their entry might be even more delayed. I am up to guessing here, though.
Warsaw falls long before the French reach the Rhine, if the French ever reach the Rhine. I lean towards Germany will keep enough troops there to stalemate any major French operations. Russia is is pretty dire shape by middle of 1916 assuming Ottomans enter war to gain land, which seems likely. Serbia falls in 1914 or early 1915. Bulgaria enters in Spring of 1915 at latest. Italy likely stays out barring some huge Conrad blunder.
Now that is the funny thing here. Whatever we assume as direct consequence of a German war plan East, we are fairly similar concerning the chain of events following a start of war following the July crisis. I would sign each of your sentences here, though I would amend that as soon as Britain would enter the war, a time-fuse on Italian participation is lit, too. Also I would like to add that Bulgaria might remain neutral if not needed against Serbia (or bribed afterwards). Perhaps Romania remains neutral, too - or joins on the CP side as soon as the Austrians move deeper into Ukraine.
In the end, I think the main opinion here is that Russia defaults a few months earlier, maximum. If that helps the CP in the end depends on other variables. So the question actually rather boils down to "how long would Britain remain neutral if Belgian neutrality is not violated (by Germany)".
I wonder though if Russia, seeing the German intensions via fortress and rail construction elects to build more railroads instead of fortresses. Completing the Murmansk railway earlier before the war would greatly ease the delivery of western supplies to Russia.
Russia was already working hard to improve its railroad network. IMHO, expecting a large scale invasion could, but doesn't necessarily lead to less emphasis on key fortifications.
Germany and Russia don't have any real reason to be involved in permanent conflict, a short undisputed border, both occupying Polish lands, no real colonial conflicts, this peace just puts a barrier to further Russian expansion in the west, keeps the Austrian empire afloat and breaks up the French-Russian alliance.
I juxtapose: heightened perception of a Germano-Slav-conflict in chauvinist circles on both sides, a by now very deeply settled Russo-French alliance causing huge diplomatic headache for Germany. And there is no guarantee that the Entente isn't back five minutes after a treaty is signed. A short border in Russian terms; in German terms its second-longest. Russian long-term goals of securing the straits which endangers German interest in the Near-East.
I would wonder if harsh terms like loss of Poland, Lithuania etc.. would only allow some Russian government to carry on the fight, either now or later, leaving Germany with hard to control territory and a permament enemy bent on revenge.
OTL's 2012 borders for Russia are harsh terms. Losing Poland would be a blessing in disguise for Russia. Even as a puppet, it would be a matter of time before it becomes a nuisance to its masters. A Kingdom of Poland would have huge territorial demands directed against Germany and, moreso, Cisleithania.
Germany could assume a Tirpitzian foreign policy goal of overseas colonies and limitations on French army sizes and weapons to ensure peace.
Yes, colonies are a cool burden around your neck and all, but are nothing the Russians can give to Germany. As in OTL, I do not expect that there is one general peace conference, but that France(+perhaps Britain) is still very well in the fight. And if Russia is beaten, France is rather the nation which needs to be offered a status quo ante peace.
Limitations on France....didn't work that well already in 1871, when Germany/Prussia tried to cripple France for decades by imposing huge reparations. Same problem with arms-control. They don't take care of themselves (the way the Poles would to a certain degree).
On Persia: I am assuming if Turkey is Central Powers at this point and Britain Allied that Germany would try to dominate Persia with the aim of controling oil fields, destabilizing India etc.. and would want some Russian acknowledgement of her involvment there.
Yes, perhaps. But still a rather hypothetical situation given German and Turkish abilities to project power over there. If the UK is within the war, Persia is out of reach. If the UK is still neutral, messing around there is an unnecessary provocation towards London.