What if Germany reversed their WWI strategy, so that instead of playing defense against Russia while they attacked France, they adopted the strategic defensive against France while they went on the offensive against Russia?

In the actual events, the French army launched attacks into Alsace-Lorraine while the German main effort on the right wing was marching through Belgium. Those attacks were soundly defeated by the economy of force German army troops that were tasked with holding the line there. So we know that the Germans could have successfully defended against French attacks.

At almost the same time (late August and early September 1914) the lesser forces the Germans had left to face the Russians destroyed to Russian field armies at Tannenberg and First Masurian Lakes. If the Germans commit the bulk of their forces to fighting the Russians, can they inflict enough losses on the Russians to force them to sue for peace, while the French are still beating themselves bloody against the German defenses in the west?

Russia had a lot more available manpower, yes, but their poor transportation system would make massing forces difficult, especially if the Germans were continually attacking along the front to keep the Russians off balance. How many defeats could the Russians handle before the either cried Uncle or they collapsed?

Without the Germans attacking neutral Belgium, does England still enter the war? (Probably, but probably not as quickly, and only after a lot of domestic political argument.) If England doesn't enter the war, that means no blockade of Germany, and thus no U-boats, and thus most likely no U.S. entry into the war. What does that mean for world history?

This would also probably put Germany in a better position at the world political level, since they could claim that they were only aiding an ally (Austria-Hungary) who was being attacked by another country (Russia) that was not party to the initial Austrian-Serbian conflict. This would especially be true if they didn't launch any major offensive against the French.

If the Russian state did collapse, or even dissolve in a vaguely orderly manner, do the Bolsheviks still come out on top? Especially if the Germans have no need to inject the Lenin virus into Russia? And if the Bolsheviks don't come to power in Russia, there's no USSR, and what does that mean for the world as we know it?

And of course, if Germany were to adopt this strategy, and the war ends with any kind of successful outcome for Germany, where does that leave Corporal Hitler? Hopefully selling crappy watercolors on a street corner in Vienna, while regailing people with tales of his wartime exploits in some Gasthof in the evenings.

Or...

If the US had stayed out of the war the 1918 flu pandemic would have forcibly ended the conflict.    And perhaps limited the spread of influenza in the western hemisphere.