Macedonia to the west of the Vardar and Bregalnitza Rivers was the only part of Turkey which adjoined Greece and Servia. Thrace, on the other hand, marched with the southern boundary of Bulgaria from the sources of the Mesta River to the Black Sea, and its eastern half was intersected diagonally by the main road from Sofia to Adrianople and Constantinople.
The real test, and the great losses, came only with the second war, when the Serbian army threw every fiber of its strength against the Bulgarians in the Battle of the Bregalnitza, one of the most stubborn struggles in military history. The result was a Serbian victory, but it was very far from being a decisive and conclusive victory.
On the same day the main body of the Bulgarians advanced down the slopes from Kustendil and took Egri Palanka, on the road toward Kumanova and Uskub. Farther south they penetrated the Valley of the Bregalnitza, the scene of the Bulgarian defeat in the Second Balkan War, where they captured the important strategic point, Sultan Tepe, and the town of Katshana, taking twelve field pieces.