The background to the wars lies in the incomplete emergence of nation-states on the European territory of the Ottoman Empire during the second half of the 19th century.
Serbia had gained substantial territory during the Russo-Turkish War, 1877–1878, while Greece acquired Thessaly in 1881 (although it lost a small area back to the Ottoman Empire in 1897) and Bulgaria (an autonomous principality since 1878) incorporated the formerly distinct province of Eastern Rumelia (1885).
All three countries, as well as Montenegro, sought additional territories within the large Ottoman-ruled region known as Rumelia, comprising Eastern Rumelia, Albania, Macedonia, and Thrace.

The First Balkan War had some main causes briefly presented below:
The Ottoman Empire was unable to reform itself, govern satisfactorily, or deal with the rising ethnic nationalism of its diverse peoples.

The Italo-Ottoman war of 1911 and the Muslims' rebellions of Kosovo and Albania showed that the Empire was deeply "wounded" and unable to strike back against another war.

The Great Powers quarreled amongst themselves and failed to ensure that the Ottomans would carry out the needed reforms.
This led the Balkan states to impose their own solution.

The Christian populations of the European part of the Ottoman Empire were  severely oppressed by the Ottoman Reign, and thus the Balkan States were forced to take action.

Most importantly, the Balkan League was formed, and its members were confident that under those circumstances an organised and simultaneous declaration of war to the Ottoman Empire would be the only way to protect their compatriots and expand their territories in the Balkan Peninsula.
The background to the wars lies in the incomplete emergence of nation-states on the European territory of the Ottoman Empire during the second half of the 19th century. Serbia had gained substantial territory during the Russo-Turkish War, 1877–1878, while Greece acquired Thessaly in 1881 (although it lost a small area back to the Ottoman Empire in 1897) and Bulgaria (an autonomous principality since 1878) incorporated the formerly distinct province of Eastern Rumelia (1885). All three countries, as well as Montenegro, sought additional territories within the large Ottoman-ruled region known as Rumelia, comprising Eastern Rumelia, Albania, Macedonia, and Thrace.
The First Balkan War had some main causes briefly presented below:
The Ottoman Empire was unable to reform itself, govern satisfactorily, or deal with the rising ethnic nationalism of its diverse peoples.
The Italo-Ottoman war of 1911 and the Muslims' rebellions of Kosovo and Albania showed that the Empire was deeply "wounded" and unable to strike back against another war.
The Great Powers quarreled amongst themselves and failed to ensure that the Ottomans would carry out the needed reforms. This led the Balkan states to impose their own solution.
The Christian populations of the European part of the Ottoman Empire were  severely oppressed by the Ottoman Reign, and thus the Balkan States were forced to take action.
Most importantly, the Balkan League was formed, and its members were confident that under those circumstances an organised and simultaneous declaration of war to the Ottoman Empire would be the only way to protect their compatriots and expand their territories in the Balkan Peninsula.
Balkan Wars