Agreed with the above. A Russo-German alliance going into the equivalent of WW1 to me is just about unbeatable. And an easy POD exists, but it’s one that has to take place in the late 19th century to predate the cozy Franco ventures. Either have Bismarck avoid one glaring mistake in choosing A-H in 1879 or find a way to continue Reinsurance Treaty until a political environment can be cultivated as to transform it into a public relationship/alliance. It's much hard to even theorize a way for them to lose a continental war as long as the alliance holds. For starters, like mentioned this is going to be a one front war for Germany after the Hapsburgs are dispatched. Likely after this central front theater resolved you will have several former Hapsburg Slavic regions bolster the ranks of Germany and Russia even further. With such an alliance you are going to add the manpower of the entire Russian Empire to German forces. That empire is going to be fed technology, industrial assistance, and military partnership as well. Add to that is the fact that you basically eliminate most of the reasons for the Revolution so we are likely not to see a Russia familiar to OTL at all.
Germany secure in her single front, supplied with resources from Russia, boosted by manpower ... will be very difficult for whatever can be stacked against them. Say you have the UK, France, Austria, Italy, the Turks, and even Romania ... I don't see them being able to win under any normal scenario of a Russian, German, Serbian, Bulgarian heavy weight alliance. Even if you find a way to isolate one of the two such as seeing the Russians run off and get caught in some kind of quagmire chase for Constantinople, leaving Germany to face the entire front alone I would still wager on German victory.
Like the question above ... Would there be a war? A-H would have to be forced into such a war as she has to know certain defeat is at her doorstep (literally) and thus I tend to think a war around this time is avoided. In such a peace time Germany puts more and more pressure on A-H until she implodes in separatist movements while Russia is free to keep pressuring the Turks and encroaching little by little supporting various parts of the Ottoman regime to rebel. The French continually backed against the wall (Atlantic) and with fewer and fewer geopolitical options are in a very difficult position. Possibly desperately cultivating emergency relationships with Spain (?) and trying in vain to bring the UK into a full military alliance.
The British eventually probably have to turn their attention west to the US and working to grow a new strategic partnership with a counter Anglo-American sphere of power to the Russo-German one. If war breaks out I don't see good things for France coming out of it and the end result being a Western Europe dominated economically (if not politically) by Germany and Russia carving up and steering the Balkans and Anatolia under her wings and potentially turning interest and eyes onto China. If the two play nice, then things work out for them. If they turn on each other ... that would be one hell of a fight.
I'll have to disagree with most of the thread here as it arguably makes Germany and Russia's position. We have to remember that Germany went with Austria over Russia for a reason. It changes the whole diplomatic picture and small details that certainly add up. I hate to quote myself but I have to add that...
~There are a ton of threads of why a quick victory against France is difficult with Germany's 1914 plan... so that leaves a quick plan against AH?
~AH has a worse position but much better army as OTL France loaned millions of francs to Russia to assist it in speeding up industrialization and infrastructure... money that will be going to AH who OTL did the heavy lifting against Russia early in the war when Germany sent 90% of it's forces to France. ITTL we have a weaker Russia and stronger AH.
~AH will not just implode from internal troubles right away - take a look at the main minorities
*Czechs - okay they are arguably the most noisy.
*Polish Galatians - will support AH because of the opposing sides - both Germany and Russia oppose any Polish power.
*Slovenes, Slovaks - relatively quiet.
*Croats - not knowledgeable to know about it.
*Magyars - have their own thing going on, what is there to complain about?
~Italy will stay probably neutral despite it's claims against the Allies as it has a
worse position than AH - the southern part will be isolated against rails, with a peninsula country being totally blockaded on all sides - both land and sea. No naval admiral would support an alliance with this Russian-German alliance.
~Russia's position is worse. Fights many fronts. Less capital from France (who Germany will not make up with) means less everything nationally built from Russia.
~There will be no "gang-pile" of the Balkans against AH - it does not make any diplomatic sense. There seems to be a mentality that just because they were Slavic Orthodox (not always the case...) that they are immediately allied against the OE and AH and with Russia. A popular PoD is Bismark going pro-Russia at the Berlin-Conference creating a super Bulgaria but recall the Bulgarians did not want to be a client of anyone
*Serbia - formerly a client state of AH before the Balkan Wars - there was a war in which if Bulgaria did not leave the Serbs alone, AH would be willing to intervene on their behalf. Certainly on the French-AH side here (the Balkan Wars dramatically changed the Balkan's geopolitics where Serbia became increasing pro-Russian.)
*Greece - a British ally with no reason to change here.
*Romania - held territorial ambitions against AH, Russia, and Bulgaria in that particular order. It was split on what to do so it joined opportunistically against AH OTL which failed it drastically. Had a pro-French populace and a Pro-Austrian king which would put it in....
*Bulgaria - joined in 1915 after see Germany do pretty good, Serbia about to collapse and the Ottoman Empire securing it's Eastern flank. Did not like Russia OTL and was an ally of AH. Many PoDs can change this but it is a toss up leaning Germany/Russia. What happens if it went with them? See Romania OTL.
~Britain will be shitting it's pants and will do everything possible to to keep the balance of power. This means
Japan (who it went alone against 9 years ago and LOST), Afghanistan, Ottoman Empire in Allies on day 1 with possibly a BEC in AH. This means a four front war for Russia which is around as bad as AH.
~The Ottoman Empire's OTL position was like AH ITL - fighting at least two fronts. Considering it's circumstances, the OE did very well and is certain to win against Russia here (being heavily supplied by the Brits)
~Why would Germany ally with Russia over it's fellow German brother nation to the south? Let us assume that it goes towards this German-Russian curb stomp of AH/France that is suggested with all the details many seem to ignore. What does Russia have to gain from this? Galicia from AH? What does Germany gain from this? Everything. No, I don't see a Russian leader looking at this alliance with much to gain - Galicia and a bigger Bulgaria (popular PoD) to leave itself alone with Pax Germanica in Europe.
Germany went with AH for a reason as did France with Russia. There seems to be a double standard that OMG AH WILL FAIL!!111 while everyone on the Russo-German side does well - a wank seen over and over in these TL.