The Congress of Berlin (June 13 –July 13, 1878) is a meeting of the representatives of six great powers of the time (Russia, Great Britain, France, Austria-Hungary, Italy and Germany), the Ottoman Empire and four Balkan states (Greece, Serbia, Romania and Montenegro).

It aims at determining the territories of the states in the Balkan peninsula following the Russo-Turkish War of 1877–78 and comes to an end with the signing of the Treaty of Berlin, which replaces the preliminary Treaty of San Stefano, signed three months earlier between Russia and the Ottoman Empire.

German Chancellor Otto von Bismarck, who leads the Congress, undertakes to stabilize the Balkans, recognize the reduced power of the Ottoman Empire and balance the distinct interests of Britain, Russia and Austria-Hungary.

At the same time, he tries to diminish Russian gains in the region and to prevent the rise of a Greater Bulgaria.

As a result, Ottoman lands in Europe decline sharply, Bulgaria is established as an independent principality inside the Ottoman Empire, Eastern Rumelia is restored to the Turks under a special administration and the region of Macedonia is returned outright to the Turks, who promise reform.

Romania achieves full independence; forced to turn over part of Bessarabia to Russia, it gains Northern Dobruja. Serbia and Montenegro finally gains complete independence but with smaller territories, with Austria-Hungary occupying the Sandžak (Raška) region.

Austria-Hungary also takes over Bosnia and Herzegovina, and Britain takes over Cyprus.

The results are first hailed as a great achievement in peacemaking and stabilization.

However, most of the participants are not fully satisfied, and grievances on the results will fester until they explode n the First and the Second Balkan wars in 1912–1913 and eventually the First World War in 1914.

Serbia, Bulgaria and Greece make gains, but all received far less than they think that they deserve..
 

The Ottoman Empire, at this time called the "sick man of Europe", is humiliated and significantly weakened, which makes it more liable to domestic unrest and more vulnerable to attack.

Although Russia had been victorious in the war that occasioned the conference, it is humiliated  here and resents its treatment.

Austria gains a great deal of territory, which angers the South Slavs, and will lead to decades of tensions in Bosnia and Herzegovina.

Bismarck becomes the target of hatred by Russian nationalists and Pan-Slavists, and he will find that he has tied Germany too closely to Austria-Hungary in the Balkans.

In the long run, tensions between Russia and Austria-Hungary intensify, as does the nationality question in the Balkans.

The congress is aimed at revising the Treaty of San Stefano and at keeping Constantinople within Ottoman hands.

It effectively disavows Russia's victory over the decaying Ottoman Empire in the Russo-Turkish War.

The congress returns territories to the Ottoman Empire that the previous treaty had given to the Principality of Bulgaria, most notably Macedonia, thus setting up a strong revanchist demand in Bulgaria, leading in 1912 to the First Balkan War.