Russia
Astro-Hungary declared war on Serbia. In turn Russia came to Serbia's aid with a few other countries.
Croatia, Slovenia, Serbia, BiH and Montenegro were once Yugoslavia.
Russia was compelled to aid Serbia against Australia.
Russia came to the aid of Serbia because they were slavs and the Czar felt a special kinship to Serbia and not Austria-Hungary. Austria-Hungary were allied with the Ottoman Empire, Germany and Bulgaria. Serbia wanted its independence from the Hapsburgs and knew that the Romanovs would support them militarily.
french :)
When Russia found out that Austria-Hungary was declaring war on Serbia, they came into alliance with Serbia for several reasons.
Yes, Serbia is a country.
Serbia
France, the Netherlands, and Spain
Austria Hungary is a country composed of many different ethnic groups ruled by the duke. Serbia was the country that backed up any nationalist movements by the ethnic groups to break free of Austria. After the Black Hand(a nationalist group) assassinated the Arch Duke and princess of Austria, Austria blamed their neighbor country Serbia because of their support for nationalists inside Austria. When this happened Russia, basically Serbia's big brother figure (in fact, they are closely related because they share allot of the same ethnicity) came to Serbia's aid. Germany, an ally of Serbia, that had been militarizing upto this point backed up Austria in order to "defend its Ally".
No. Serbia is a country in Europe.