Why did Russia mobilize in 1914?

[Anthony EJW]

1.) It was not necessary to mobilize armies that were on the German border to protect Serbia. Any threat towards Austria-Hungary could have been made by armies opposing Austria-Hungary exclusively.
2.) A full mobilization meant war with Germany - Russia had the choice to avoid this war and did not so in the full knowledge of the consequences (thats what an ultimatum is for). It forced Germany to either wait until Russia was fully mobilized and any conflict lost or go to war asap. Given the strategical overall situation this made the choice for Germany clear and inevitable.
3.) There was no treaty between Serbia and Russia that forced Russia to protect them.
4.) The Tzar was very caustious as regards the war; and was still worried about revolutions
5.) Russia's reorganisations (modernisation of border forts, better equipment for the army, and increasing the size of the rail networks to allow for quicker mobilization) would not be complete until at least 1917.

So why did Russia mobilize to support Serbia; and further why did they mobilize on the Russo-German border as well which would antagonize Germany?

[Loki]

Serbia was a friend of Russia and the Serbian army wasn't able to defend its country against the Austro-Hungarian army. So the Zar mobilized his army to protect serbia. He hoped, that the declaration of war against Austro-Hungarian would stop them in their attack against Serbia. He also mobilized his forces at the german border, because he was informed that Germany was an allie of Austria and would attack russia if he would support serbia. It would been only a matter of time.

[fdewaele]

It was because of the alliances. If Russia interfered in the Austrian-Serbian war, it would automatically have brought Germany into the war to equalize the Russian entry, therefore not mobilizing on the German front was sheer lunacy and even the Russians weren't that dumb.

[Loki]

Just that i said.

[Spearhead]

And besides, all of the bigwigs in Russia, Germany, France and A-H thought they could and would win quickly. They'd been spending immense sums on armament, they had put more men under arms than their precedessors on the thrones and high seats had combined... why, it's impossible that we lose. Look at out magnificent army and our powerful allies. The enemy must be mad to go to war against us.

[Feanor]

Another reason why they mobilized was because they thought that if they failed Serbia, their other small allies and uncommitted nations would go away from/not join their camp.

[ph404]

The initial Russian mobilisation was only partial --- 4 military districts (Kiev, Odessa, Moscow, Kazan) and the Black Fleet.This was aimed against Austria-Hungary.As it had no major impact in detering Vienna full mobilisation,including the Baltic and Warsaw districts followed.