Bulgaria was part of the Ottoman Empire until it became independent in 1908. It was bordered by Romania to the North, Greece to the South, Serbia to the West and the Black Sea to the East.

Following independence, Prince Ferdinand declared himself ‘Tsar of all the Bulgarias’ and sought to further his territorial ambitions by military expansion – earning Bulgaria the nickname ‘Prussia of the Balkans’.

Bulgaria’s frontiers were fixed by the Treaty of Bucharest in 1913.

Prelude to war

MFQ 1/391/4

Detail from a map of Istanbul (Constantinople), 1918 MFQ 1/391/4

Following its independence from Ottoman rule in 1908, the Bulgarian government wanted to unify various territories that were still under Ottoman rule but were populated by ethnic Bulgarians. One of these territories was Macedonia which was in open rebellion against the Ottoman Empire.

In October 1912, war broke out between the Ottoman Empire and the Balkan states (Bulgaria, Greece, Serbia, and Montenegro) with Bulgarian forces advancing to within 40 kilometres of Constantinople (FO 373/2/2).

As a result of the war, almost all remaining European territories of the Ottoman Empire were captured and the territory divided between the victorious Balkan states.

The war ended in May 1913 with the Treaty of London that sought to negotiate new boundaries that all parties could agree to (FO 881/10564).

The borders of Macedonia and Albania remained contested.

In June 1913, war began again with Bulgaria mounting a surprise attack on Serbia and Greece. Montenegro, Rumania (now Romania) and the Ottoman Empire joined the conflict, siding against Bulgaria.

Faced with almost certain defeat, Bulgaria sued for peace. This resulted in the Treaty of Bucharest in which Bulgaria lost almost all the territory it had gained earlier (FO 881/10299X).

The failure to create a unified Bulgarian state led to an influx of ethnic Bulgarian refugees from Greece and Macedonia and turned the Bulgarian government against Russia whom it blamed for deserting it in its time of need.

Bulgaria's war

MFQ 1/391/1

Hand bill marked up as small square 'Greeks in Thrace' MFQ 1/391/1

In the months following the outbreak of the First World War, Bulgaria observed a strict policy of neutrality.

This position reflected deep divisions in the country; the Tsar and the government were supportive of the Central Powers with the army largely pro-Russian. Despite differences, there was universal support within the country for Bulgaria to re-gain lost territory in Macedonia.

As the war progressed, all sides sought to recruit Bulgaria to their cause. Bulgaria’s strategic position and strong military made it a powerful potential ally for whichever side managed to win its support. The British Foreign Secretary Sir Edward Grey was ‘not unsympathetic to Bulgaria’s claims if large additions of territory were acquired from other states as a result of the war’ (FO 371/1901).

The concessions promised by Germany and the Hapsburg Empire (which included the virtual dismemberment of Serbia) proved irresistible and in September 1915, Bulgaria entered into an alliance with the Central Powers.

On 14 October, following general mobilisation, the Bulgarian Army invaded Serbia and within six weeks the country was overrun (FO 371/2273). By the end of the year, the whole of Serbia was occupied by the armies of the Central Powers with Bulgaria in control of Macedonian territory to the Vardar River.

The Bulgarian advance made it impossible for the Allies to continue to defend Gallipoli, and the last troops withdrew in January 1916 (WO 106/1357).

In 1917, following concerted diplomacy, Greece entered the war on the Allied side.

In 1918, the multi-national Allied Army of the Orient, based at Thessaloniki in northern Greece, launched an offensive which broke through on the Macedonian front (WO 95/5492). It was now clear that the Allies would win the war and on 29 September 1918 Bulgaria surrendered.


FO 925/21109

Bulgaria. Map accompanying the Treaty of Peace between the allied and associated powers and Bulgaria FO 925/21109

On the losing side, Bulgaria was forced to accept a punitive peacetime settlement.

It lost its Macedonian territories to the new state of Yugoslavia and its Aegean and Black Sea coastlines to Greece and Romania, respectively (FO 388/2).

On top of its territorial losses, Bulgaria had to pay reparations of $450 million over 38 years and reduce the size of its army to 33,000 men (FO 608/31/6). The harsh conditions led to political instability with Tsar Ferdinand abdicating in favour of his son Boris III.

In 1923 the Prime Minister was assassinated by nationalists and the country descended into civil war with the Bulgarian Communist Party, supported by the Soviet Union, pitted against the nationalist Internal Macedonian Revolutionary Organisation (IMRO).

In an attempt to restore stability, Tsar Boris banned all political parties and declared martial law (FO 371/8569).

Key documents

FO 388/2

Peace Treaties FO 388/2

  • Balkans (War). Code W19 / Code 19W File 38540 (papers 43088-66807), 1914. Document reference FO 371/1901
  • Peace Conference of 1919 to 1920: Handbooks, Bulgaria, November 1918. Document reference FO 373/2/2
  • Embassy and Legation, Bulgaria (formerly Ottoman Empire): General Correspondence, peace treaties, 1919-1920. Document reference FO 388/2
  • Bulgaria: Desiderata, including: terms to be imposed on Bulgaria, 1919. Document reference FO 608/31/6
  • Balkan states and Turkey: Treaty of peace between Bulgaria, Greece, Montenegro, Persia and Turkey, Treaty of London, 30 May 1913. Document reference FO 881/10564
  • Bulgaria: Treaty of peace between Bulgaria and Greece, Montenegro, Roumania and Servia (Bucharest), 18 August 1913. Document reference FO 881/10299X
  • Unit War Diaries, Allied Armies of the Orient, December 1918 – May 1920. Document reference WO 95/5492
  • Military Situation, Bulgaria: Intelligence Notes, December 1916. Document reference WO 106/1357