Well during the Russo-turkish War the Russians were winning the war and were about to take the Turkish capital of Istanbul and finally realize the long held Russian dream of gaining permanent access to the Mediterranean. In essence the Russians were going to create a "greater Bulgaria" out of the captured Turkish territory in the Balkans that would essentially be nothing more than a puppet state, which would cement Russia's influence in the Balkans. Now all this being said the main opposers of this expansion of Russian influence in the balkans were Britain and Austria-Hungary. The British had been propping up the Ottomans since the middle of the 19th to counter Russian gaining any route to the Mediterranean, which was largely under the sphere of influence of the British and french. the British were especially fearful because the Mediterranean was the route to the Suez canal which led to India- the jewel of British empire. As for the Austrians the Hapsburg Empire had a significant slavic population and Russia had primarily fought the Russo-Turkish War in the name of pan-slavism, to liberate their slavic brothers from the yoke of the Turk. As such the Austrians feared any sources that might fan the flame of nationalism among the slavic population within their empire. Nw it looked like the British and the Austrians were gearing up to go to war over this issue which brought in our final player- Germany. The german Chancellor Otto von Bismarck had always attempted to keep Germany in the Russians good graces, and to have Austria going to war with Russia would drag Germany into the war on the side of the Austrians (who were the Germans principle ally). As such Bismarck presented Germany as an "honest broker" with no real interests in the matter, in order to prevent a European War, and proposed to hod a conference in Berlin. Under the terms reached at the Congress Austria would occupy the turkish provinces of Bosnia-Herzegovina, a smaller Bulgaria would be created that would be an autonomous vassal of the Ottomans, Romania, Serbia, and Montenegro would become independent, and Russia would receive a sliver of territory in Bessarabia. Basically, Bismarck hoped by dividing up the Balkans, he could stabilize the Balkans and prevent a large European war over the matter. He always said that the next widespread war in Europe would be fought over some "damn silly thing in the Balkans." all in all the congress left a bitter taste in everyones mouth with nobody really being happy about it, and the unresolved issues would eventually come to a head some 30 years later with the first world war. Thats just a general background of the congress as for the nitty gritty of Bulgarian politics I don't have much but I hope this helped.