firstly "austria & Hungary declared was on Serbia" does not make sense but austria & Hungary declared war on Serbia in the year 1914.
In 2006. when Montenegro declared independence.
Russia
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...
Austria Hungary declared war on Serbia.
Serbia
Serbia was in WWI because Austria-Hungary declared war on them.
Serbia Serbia
Montenegro declared independance from serbia on 3. june 2006.
Austria-Hungary, declared war on Serbia
Austria-Hungary declared war on Serbia at the start of World War I.
Mobilized its military because of its alliance with Serbia.
No, they are allies for ages.