Nationalism and Imperialism
Nationalism: It is a political ideology characterized by the promotion of the interest of a particular Nation and allegiance to Nations. It aims to gain and maintain sovereignty.
Imperialism : It is an ideology underwhich a strong Nation rules over Weak Nations.
Balkan Region
The most serious source of nationalist tension in Europe after 1871 was the area called the Balkans.
The Balkans was a region of geographical and ethnic variation.
It comprises of modern-day Romania, Bulgaria, Albania, Greece, Macedonia, Croatia Bosnia-Herzegovina, Slovenia Serbia and Montenegro whose inhabitants were broadly known as Slavs.
A large part of the Balkans was under the control of the Ottoman Empire.
Nationalism, aligned with imperialism in the Balkan region led Europe to disaster[First World War] in 1914.
Balkan Tension [Factors/Reasons]
Nationalism
A large part of Balkans was under the Ottoman Empire and its disintegration created explosive situation.
Balkan peoples (countries) with the ideas of romantic nationalism and shared history claim their Independence.
Greek Independence became an inspiration.
One by one its European subject Nationalised broke away from its control and declared independence.
They were also jealous of each other has started fighting with adjacent territories to expand their territories.
[Note: The above points are applicable for the reasons of nationalists tensions after 1871 and struggle of Slav nationalities]
Imperialism
Imperialism also intensified the region due to power rivalry between imperial nations.
Each power - Russia, Germany, England and Austria-Hungary wanted to establish their power and control in the region and started fighting with each other.
Due to the intense rivalry among the European powers over trade and colonies as well as naval and military might led to a series of wars and finally the First World War.