The Second Balkan War (29 June – 10 August 1913) was a conflict fought between the Tsardom of Bulgaria and its former Balkan League allies, Serbia, Montenegro and Greece, who were later joined by Romania and the Ottoman Empire.
The war began when Bulgaria, unhappy with the division of territory in Macedonia after the First Balkan War, launched attacks on Serbian and Greek forces, who repelled the offensive and pushed into Bulgarian territory. With most of Bulgaria's army committed in the south, Romania intervened from the north. The Ottoman Empire also took advantage of the situation to recover territories lost the previous year.
As Bulgaria suffered military setbacks on multiple fronts and Romanian forces advanced towards its capital, Sofia, it requested an armistice. The war ended with the Treaty of Bucharest, which compelled Bulgaria to cede significant territory: Southern Dobruja to Romania, parts of Macedonia to Serbia and Greece, and Adrianople (Edirne) to the Ottoman Empire under the separate Treaty of Constantinople.
The war altered the political balance in the Balkans and intensified regional tensions. Serbia expanded its territory and influence, heightening its rivalry with Austria-Hungary. Bulgaria, weakened by defeat and territorial losses, would later align with the Central Powers in the First World War.
Background
During the First Balkan War, which began in October 1912, the Balkan League (Bulgaria, Serbia, Montenegro and Greece) succeeded in driving out the Ottoman Empire from its European provinces (Albania, Kosovo, Macedonia, Sandžak and Thrace), leaving the Ottomans with only East Thrace. The Treaty of London, signed on 30 May 1913, which ended the war, acknowledged the Balkan states' gains west of the Enos–Midia line, drawn from Midia (Kıyıköy) on the Black Sea coast to Enos (Enez) on the Aegean Sea coast, on an uti possidetis basis, and created an independent Albania.
However, the relations between the victorious Balkan allies quickly soured over the division of the land, specifically in Macedonia. During the pre-war negotiations that resulted in the Balkan League's establishment, a secret agreement on 13 March 1912 was signed by Serbia and Bulgaria, which determined their future boundaries, effectively sharing northern Macedonia. In case of a post-war disagreement, the area to the north of the Kriva Palanka–Ohrid line (with both cities going to Bulgaria) had been designated as a "disputed zone" under Russian arbitration, with the area to the south of this line assigned to Bulgaria. During the war, the Serbian army succeeded in capturing lands in Macedonia, which were promised to Bulgaria according to the March 1912 treaty, and started to harass the Bulgarian population in the region. At the same time, the Greek army advanced north, occupying Thessaloniki shortly before the Bulgarian army had arrived, and established a common Greek border with Serbia.
When Bulgaria called upon Serbia to honour the pre-war agreement over northern Macedonia, the Serbian side, displeased at the Great Powers' requiring them to give up their gains in north Albania, adamantly refused to evacuate any more territory. These developments ended the Serbian–Bulgarian alliance and made future war inevitable. Soon, Bulgarian troops started minor clashes along the borders of the occupation zones of Serbia and Greece, due to which the two started alliance negotations, perceiving Bulgaria as a threat.
On 19 May/1 June 1913, two days after the signing of the Treaty of London and just 28 days before the Bulgarian attack, Greece and Serbia signed a secret defensive alliance, confirming the current demarcation line between the two occupation zones as their mutual border, promising that neither side would make a separate settlement with Bulgaria and concluding an alliance in case of an attack. With this agreement, Serbia succeeded in making Greece a part of its dispute over northern Macedonia, since Greece had guaranteed Serbia's current (and disputed) occupation zone in Macedonia. In an attempt to halt the Serbo-Greek rapprochement, Bulgarian Prime Minister Geshov signed a protocol with Greece on 21 May, agreeing on a permanent boundary between their respective forces, effectively accepting Greek control over southern Macedonia. However, his later dismissal ended the diplomatic targeting of Serbia.
Another point of friction arose when Bulgaria refused cede the fortress of Silistra to Romania. When Romania demanded its cession after the First Balkan War, Bulgaria's foreign minister offered instead some minor border changes, which excluded Silistra, and assurances for the rights of the Aromanians in Macedonia. Romania threatened to occupy Bulgarian territory by force, but a Russian proposal for arbitration prevented hostilities. In the resulting Protocol of St. Petersburg of 9 May 1913, Bulgaria agreed to give up Silistra. The resulting agreement was a compromise between the Romanian demands for the city, two triangles at the Bulgaria–Romania border and Balchik and the land between it and Romania and the Bulgarian refusal to accept any cession of its territory. However, the fact that Russia failed to protect the territorial integrity of Bulgaria made the Bulgarians uncertain of the reliability of the expected Russian arbitration of the dispute with Serbia. The Bulgarian behaviour also had a long-term impact on Russo-Bulgarian relations. The uncompromising Bulgarian position to review the prewar agreement with Serbia during a second Russian initiative for arbitration finally led Russia to cancel its alliance with Bulgaria.
In 1912, Bulgaria's national aspirations, as expressed by Tsar Ferdinand and the military leadership, exceeded the provisions of the 1878 Treaty of San Stefano, considered even then as maximalistic, since it included both Eastern and Western Thrace and all Macedonia with Thessaloniki, Edirne and Constantinople. Early evidence of the lack of realistic thinking in Bulgarian leadership was that although Russia had sent clear warnings expressed for the first time on 5 November 1912 (well before the First Battle of Çatalca) that if the Bulgarian army occupied Constantinople they would attack it, they continued their attempts to take the city.
By mid-June, Bulgaria became aware of the Serbian–Greek agreement. On 27 June, Montenegro announced that it would side with Serbia in the event of a Serbian–Bulgarian war. On 5 February 1913, Romania had settled her differences over Transylvania with Austria-Hungary, signing a military alliance, and on 28 June, officially warned Bulgaria that it would not remain neutral in a new Balkan war.
As skirmishing continued in Macedonia, mainly between Serbian and Bulgarian troops, Tsar Nicholas II of Russia tried to stop the conflict since Russia did not wish to lose either of its Slavic allies in the Balkans. On 8 June, he sent an identical personal message to the Kings of Bulgaria and Serbia, offering to act as arbitrator according to the provisions of the 1912 Serbo–Bulgarian treaty. Serbia was asking for a revision of the original treaty since it had already lost north Albania due to the Great Powers' decision to establish the state of Albania, which had been recognized as Serbian territory under the prewar Serbo–Bulgarian treaty, in exchange for Bulgarian expansion in northern Macedonia. The Bulgarian reply to the Russian invitation contained so many conditions that it amounted to an ultimatum, leading Russian diplomats to realize that Bulgaria had already decided to go to war. That caused Russia to cancel the arbitration initiative and angrily repudiate its 1902 treaty of alliance with Bulgaria. Russia's Foreign Minister Sazonov's exact words to Bulgaria's new Prime Minister Stoyan Danev were "Do not expect anything from us, and forget the existence of any of our agreements from 1902 until the present". Bulgaria was shattering the Balkan League, Russia's best defence against Austro-Hungarian expansionism, a structure that had cost Russia much blood, money and diplomatic capital during the previous 35 years. Then Serbia and Greece proposed that each of the three countries reduce its army by one-fourth as a first step to facilitate a peaceful solution, but Bulgaria rejected it.
Preparation
Bulgarian war plans
Assistant Commander-in-Chief General Mihail Savov, with the help of Colonel Stefan Nerezov, drafted on 31 May plans for an eventual war with both Serbia and Greece. According to the Savov-Nerezov Plan, the First Army under General Vasil Kutinchev was to advance toward Knjaževac and Zaječar in the Timok Valley, after which it was to march as fast as possible toward Pirot and Bela Palanka and join up with the Third Army. The Third Army under General Radko Dimitriev was tasked with tying down the Serbian forces near Pirot, leaving a covering force in the direction of Niš, and, after awaiting the arrival of the First Army, attacking and capturing Pirot. The two united armies were then expected to advance along the Morava valley toward Vranje and Kumanovo and there deliver a decisive blow against the main Serbian forces concentrated at Ovče Pole. The Cavalry Division was to operate on the right flank of the Third Army, linking it with the First Army. The Fifth Army, under General Stefan Toshev, was supposed to serve as the "axis of rotation" of the entire Bulgarian army, drawing as many enemy forces as possible into the sector Sultan Tepe–Kriva Palanka–Mount Kitka.
The biggest Bulgarian Army, the Fourth, under General Stiliyan Kovachev, was to advance in the Štip–Zletovo sector and capture the Serbian forward positions, while its left wing had to drive the enemy behind the Vardar River. After establishing itself in the aforementioned positions, the Fourth Army was to force-march four brigades to the Second Army, under General Nikola Ivanov, to join the operations against the Greeks. After awaiting the appearance of the First and Third Armies, the bulk of the Fourth Army, still positioned in Vardar Macedonia, was to go on the offensive and join the combined operations of the First, Third, and Fifth Armies and decisively defeat the Serbian army.
The Second Army was required to advance with the 11th Division and fortify itself along the Aegean coast and the left bank of the Struma River. The right wing had to seize Gevgelija, while its centre, reinforced by the Serres Brigade and elements of the 11th Division, had to occupy favourable starting positions for a general advance toward Thessaloniki after the arrival of the four brigades from the Fourth Army. Savov's overall strategic concept was for a fast and decisive blow against the Serbian army, which he thought was the main military danger for the Bulgarian army, while the reinforced Second Army had to push the Greek army out of Thessaloniki. Savov relied on the speed of the action to take out Serbia and Greece before Romania and the Ottoman Empire could intervene, which he presumed would not dare to go to war against a victorious Bulgaria.
On the other hand, Chief of Staff of the Active Army, General Ivan Fichev, while opposing a new war, criticised Savov's plan for lacking a concentrated large force capable of delivering a decisive blow, underestimating the geographical obstacles that would arise during the flanking maneuver through the Morava valley and the doubtful ability of the Second Army to hold off the Greek army on such a wide front. Fichev instead argued for reinforcing the Bulgarian armies facing the Greeks and delivering a crushing blow there, while maintaining a defensive posture against the Serbs. Only after the Greek army had been put out of action could enough forces be sent against the Serbian army for a decisive confrontation there.
The Savov–Nerezov Plan, however, was never officially approved, which meant that virtually all commanders of the Bulgarian Army lacked a clear picture of the operational plan of the High Command and of what their respective armies were supposed to do in the event of a future war. A point of friction arose between the commander of the Second Army and Savov over clear directions, reinforcements and formations being understrength and overstretched on the Greek front, with Savov greatly underestimating the capabilities of the Greek army.
Greek–Serbian Alliance and war plans
After signing the Greek-Serbian alliance, military representatives of Serbia, Colonels P. Pešić and D. Tufegdžić, and of Greece, Captain K. Stratigos, drew up a military convention and an operational plan against Bulgaria in the event of a future war. The overall strategic objective was the destruction of Bulgarian military power and the enforcement of Serbian and Greek demands on Bulgaria. The Serbian-Greek plan envisioned three possible scenarios: