For the following reasons, Balkans was the most serious source of nationalist tension in Europe after 1871:
(1) Balkans was a region of geographical and ethical variations comprising modern-day Romania, Bulgaria, Albania, Greece, Macedonia, Croatia, Bosnia-Herzegovina, Slovenia, Serbia and Montenegro whose inhabitants were known as Slays.
(2) A large part of the Balkans was under the control of the Ottoman Empire. The spread of the ideas of romantic nationalism in the Balkans together with the disintegration of the Ottoman Empire made this region very explosive.
(3) As the different Slavic nationalities struggled to define their identity and independence, the Balkan area became an area of intense conflict.
(4) The Balkan states were jealous of each other and each hoped to gain more territory at the expense of other. Balkans also became an area of big power rivalry.
(5) Each European power such as Russia, Germany, England, and Austria-Hungary was keen on countering the hold of other powers over the Balkans and this led to a series of wars eventually the First World War.