Milan's political troubles were further increased by the defeat of the Serbians in the war against Bulgaria from 1885–1886. In September 1885, the union of Eastern Rumelia and Bulgaria caused widespread agitation in Serbia. Milan promptly declared war upon the new Bulgarian state on 15 November. After a short, decisive campaign, the Serbs were utterly routed at the Battle of Slivnitsa and at the Battle of Pirot. Milan's throne was only saved by the direct intervention of Austria-Hungary. Domestic difficulties now arose which rapidly assumed political significance.