In terms of treaties, Russia had a treaty with France but this would not have been activated by Austro Hungary attacking Serbia. The problem was that on the 25 of May 1914, the Imperial Council in Russia decided to support Serbia. Austro Hungary declared war on Serbia and at this point Russia started to mobilize. Germany then declared war on Russia and it....
Do you have certain source on Imperial Council's declaration? How could it have been declared in May? I am not sure if I had understood some things about chronology of those events. (I am doing on seminar on Nicholas II, therefore I must have certain information).
What happened at the Konopisht castle during Nicholas' visit to Romania in June of 1914, where Franz Ferdinand and Kaiser Wilhelm met and discussed about ' Entente's future and possible war with Russia in sooner time'.
The ultimatum was finished on July 19th in Vienna, but it was decided to send it as soon as President Poincare leaves Russia, where he had been for several days, and left Russia on July 23th. So Serbian Government got the ultimatum on July 23th. Reason for its delaying was fear of immediate collaboration between Russia and France.
The last point of the ultimatum would allow to Austro Hungarian investigation body to do the research over the Serbian territory. Simply, it couldn't have been allowed. So that A.-H. declared war on July 28th, a month after the assassination in Sarajevo. Serbian regent asked for Nicholas' help and for Russia's involvement. Nicholas replied that '
in any case, Russia will not remain indifferent towards Serbia'.
Germany declares was on August 1st 1914 (Nicholas' face turned pale), and the day after (after consultations with minister Sazonov and sir George Buchanan), Tsar agreed for mobilization, and held the famous speech at the Winter Palace balcony on August 2nd.Even the same declaration of was says that unprotected Belgrade was attacked and Russia's historical mission is protecting Slavs. Russia tried to help twice times before , in 1908/9 and in 1912/3.