How did World War I change the borders and states of the Balkans?

World War I fundamentally reshaped the Balkans by causing the collapse of the Austro-Hungarian Empire and the Ottoman Empire, which had long held competing interests in the region. The subsequent Paris Peace Conference (1919–20) redrew the map, aiming to consolidate territories into larger, more viable nation-states.12

Key changes included:

• Kingdom of Serbs, Croats, and Slovenes: Formed on December 1, 1918, this new state (later renamed Yugoslavia) united the former kingdoms of Serbia and Montenegro with South Slav territories previously under Austro-Hungarian rule, including Croatia-Slavonia, Dalmatia, Slovenia, Bosnia and Herzegovina, and the Vojvodina.13
• Greater Romania: The Romanian kingdom significantly expanded, incorporating Transylvania, Bukovina, Bessarabia, and much of the Banat region.12
• Minority Challenges: Because the new borders could not perfectly align with ethnic divisions, the settlements created complex minority issues. To mitigate instability, states were required to sign treaties guaranteeing civil rights for all citizens.12

These territorial adjustments were intended to create effective barriers against bolshevism, though the resulting ethnic diversity and the disruption of traditional economic patterns contributed to ongoing regional instability.12