“One of the primary causes of WWI was that the rules of the great power rivalry in the Balkans were not clear.”
Well, they were very clear to Austria-Hungary. They were unsure of how Russia was going to respond to developments following the assassination of Archduke Franz Ferdinand, so it — behind the scenes — sought and received from Germany assurances that if Russia declared war, Germany would have Austria-Hungary’s back, even if eventually France and Britain joined the party. With those assurances, Austria-Hungary issued Serbia an impossible ultimatum, and the game was on.
Such stupidity, on so many heads! I have long said that WWI was one of the greatest tragedies in the history of the world: It was so, so, so unnecessary.
More private agreements. Not sure the Russians would have jumped in if they knew war with Germany would immediately follow, although they were pretty cocky and did do well against Austria-Hungary until the Germans made a serious commitment.