Historical Background:
Nationalist tension emerged in the Balkans due to a complex interplay of historical, political, and social factors.

Legacy of Ottoman Rule:
The Balkans were under Ottoman rule for centuries, leading to a mix of ethnic and religious groups living in close proximity. This legacy created deep-seated divisions and grievances among different communities.

Rise of Nationalism:
As the Ottoman Empire weakened in the 19th century, nationalist movements began to emerge in the Balkans. Various ethnic groups, such as Serbs, Bulgarians, Greeks, and Albanians, sought to assert their own national identities and independence.

Imperial Rivalry:
The Balkans became a battleground for imperial powers, including Austria-Hungary, Russia, and the Ottoman Empire, seeking to expand their influence in the region. This competition further fueled nationalist tensions as different groups aligned themselves with different powers.

Wars and Revolts:
A series of wars and revolts broke out in the Balkans as nationalist movements sought to break away from Ottoman rule or assert their dominance over other ethnic groups. These conflicts intensified nationalist sentiments and deepened divisions among communities.

Assassination of Archduke Franz Ferdinand:
The assassination of Archduke Franz Ferdinand of Austria-Hungary in Sarajevo by a Bosnian Serb nationalist in 1914 triggered World War I. This event highlighted the explosive nationalist tensions in the Balkans and their potential to spark wider conflicts.
In conclusion, nationalist tension emerged in the Balkans due to a combination of historical grievances, ethnic divisions, imperial rivalries, and nationalist aspirations. These factors created a volatile environment that ultimately contributed to the outbreak of World War I.