When AH declared war on Serbia on 28th June, Russia started to mobilize it's troops on it's borders. Then Montenegro on 5th august declared war on AH, to help their brothers. Because in that time almost all population of Montenegro declared themselves as Serbs.
Austria declared war on Serbia
Austria Hungary declared war on Serbia.
After the Austro-Hungary monarchy declared war on Serbia, France and Russia who were protecting Serbia declared war on Austria-Hungary. and then Germany declared war on Russia and France, then UK declared war on Germany...
Serbia Serbia
Serbia was in WWI because Austria-Hungary declared war on them.
Austria-Hungary declared war on Serbia at the start of World War I.
Austria-Hungary, declared war on Serbia
Astro-Hungary declared war on Serbia. In turn Russia came to Serbia's aid with a few other countries.
Serbia
Russia
Austro-Hungarian Archduke Franz Ferdinand was assinated by Serbian nationalists. Austria declared war on Serbia. Russia, allied with Serbia, declared war on Austria, Germany declared war on Russia, England and France declared war on Both.
No, they are allies for ages.