WWI started on 28 July when the Austro-hungarians invaded Serbia. the others got automatically involved due to treaties (and quite frankly that’s what they wanted — the Russians wanted to crush the Ottomans and their plan in 1914, shared with the French and British was to take over Constantinople and have their sphere of influence in central/eastern europe and to reduce Austria to just the area of Salzburg.)
In 1914 also, the British sold two modern destroyers/first class naval ships to the Turks -- this was a big alarm to the Russians as this threatened Russia's bases in the Black Sea
Remember that Russia and Turkey were/are mortal enemies for centuries
Also, the Russian war preparation and conscription was humming and this alarmed the Germans -- who saw Russia as a massive threat. Well, this was the Prussian's fault for allowing the partition of the Polish-Lithuanian commonwealth -- even a weakened buffer state is better than no buffer state.
The Rzeczpospolita in the 18th century was a puppet of the Russians that is true, but it was a good buffer between the Russians and the Germanics (Prussians and Austrians).
Before its destruction the Austrians and the Russians were actually allies as they had a common enemy -- the Turks
After the partitions, Austria now had TWO enemies to the east.