Austria-Hungary

Austria-Hungary was a European kingdom, an ally of Germany. Slavic nationalism increasingly threatened to tear Austria-Hungary apart. It suffered various acts of hostility by Serbia.

After the assassination of Franz Ferdinand by a Serbian terrorist, Austria-Hungary presented Serbia with a ultimatum, giving it 48 hours to reply favorably to all its demands. Serbia accepted most—but not all—of Austria-Hungary's demands and asks for international mediation of the dispute. As Serbia had not met all the demands, Austria-Hungary rejected the mediation and declared war on Serbia.

Russia mobilized its armed forces against Austria-Hungary and Germany, resulting to Germany declaring war against Russia.