Southeast Europe
This concept is based on the boundaries of the Balkan peninsula. The countries that have been described as being entirely within the region are: Albania, Kosovo, Bosnia and Herzegovina, Bulgaria, Macedonia and Montenegro.
Balkans Campaign (World War I)
Bulgaria, recuperating from the Balkan Wars, sat out the first year of World War I. When Germany promised to restore the boundaries of the Treaty of San Stefano, Bulgaria, which had the largest army in the Balkans, declared war on Serbia in October 1915. Britain, France and Italy then declared war on Bulgaria.