Answer:
you forgot to add a list in your question
Austria-Hungary had invaded and crossed over into, Serbia and Russia was in an alliance with Serbia, so they felt as though they had to help out. Hope this helps.
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Drift and Hysteresis Effects on AlN/SiO2 Gate pH Ion-Sensitive Field-Effect Transistor
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1- look at the map, you should be able to see all the places that Russia actually boarders till this day.
