The Kingdom of Bulgaria, also known as the Tsardom of Bulgaria, was a nation located in the Balkans. After achieving independence from the Balkans in 1908, Bulgaria was heavily invested in by the Allied Coalition as a way to oppose Serbia. Hoping to unite all Bulgarians, the Tsar launched the Balkan Wars, which would escalate into World War I, which would eventually see Bulgaria defeated, and the Tsar's power would become liberated as a democratic parliament became in charge of the nation. During the Great Depression, Tsar Boris would launch a coup and regain authoritarian control over Bulgaria. Bulgaria would align with the Third French Empire and fight alongside it in World War II. Russian troops would conquer Bulgaria, abolish the monarchy, and replace with a people's republic.
The "Balkan Prussia"
Bulgaria became an autonomous part of the Ottomans in 1878 when the Principality of Bulgaria was created. Despite the expansion of Bulgarian territory, there was still a sizeable Bulgarian population that did not fall under control of the Principality. Bulgaria also desired the area of Macedonia, which was contested by Serbian and Greek claims. War with the Ottoman Empire seemed likely when the Bulgarians in Macedonia rose up in rebellion in 1903. In 1908, with the Ottomans distracted, Bulgaria declared its independence, with Ferdinand I becoming its Tsar. This was of great interest to the Allied Coalition, especially Austria-Hungary, which sought a counterbalance to Serbian power in the Balkans. With the majority of Bulgaria being rural farmland populated by farmers and peasants, Austria invested heavily in the nation, hoping to industrialize the nation quickly. While the Bulgarian military became incredibly modernized, the rest of the nation lagged behind. By 1912 Bulgaria was still behind its neighbors when it came to industrialization.Also in 1912, Bulgaria, Serbia, and Greece set aside their differences to join a pact and plan an attack on the Ottomans. Serbia made secret agreements to partition Macedonia and Thrace, also the boundaries for these partitions were left vague. After the Ottomans refused to implement reforms in this area, the First Balkan War broke out in October 12. Bulgarian troops sustained the heaviest casualties out of their pact, but had gained several impressive victories over the Ottomans. With Bulgarian troops threatening Constantinople, the Ottomans agreed to an armistice in December, but talks broke down and fighting soon resumed. Bulgaria captured Andrianople and most of Thrace, while the Serbs and Greeks occupied Macedonia.
Because of its impressive victories and highest amount casualties, Bulgaria felt it was entitled to have the biggest share of the land. Serbia refused to vacate its land in Macedonia, claiming that Bulgaria failed to achieve its pre-war objectives (capture Andrianople without Serbian help) and the parition of Macedonia needed to be revised. Serbia made a pre-emptive alliance with Greece, and promised Greece territory in Thrace in exchange for help in any upcoming conflict against Bulgaria. Enraged by this, and encouraged by the Allied Coalition, Tsar Ferdinand declared war on Greece and Serbia on June 29, 1913.
Hoping to limit Serbian power, Austria used to illegal occupation of Albania by Serbia to issue an ultimatum: Serbia and Greece must accept Bulgaria's demands, or face war. Austria intentionally made the ultimatum too harsh for Serbia to accept it in order to provoke a war. Meanwhile, the Ottomans had entered the war on the side of the Serbians, in order reclaim Bulgarian territory, resulting in an uneasy alliance between the two. Ottoman Minister of War Enver Pasha announced they would come to the defense of Serbia if Austria attacked. The Serbs refused the ultimatum, and on August 8, the First World War began with an Austrian invasion of Serbia.
World War I
With Serbian forces diverted to stave off the Russians, Bulgaria moved troops to combat the Greeks and Ottomans. A stalemate on the Greek front in the mountains and hills tied up Bulgarian forces, allowing the Ottomans to entire nearly unnopposed. The Ottomans retook Thrace, which it had lost in the First Balkan War, and carried out ethnic cleansing there. Over 500,000 Bulgarians would either exterminated or forced to flee, essentially the entire Bulgarian population of Thrace.
Meanwhile, Bulgarian forces had broken through Greek lines in the hills, and began to make gains into Macedonia. The 3 fronts - Serbia, Greece, and Ottoman - soon became static with trench warfare. As the war went on it became unpopular with the majority of the Bulgarian people. The Bulgarian peasants - unified under a movement known as the Agrarian Union - suffered economic hardship. The government, under Prime Minister Vasil Radoslavov, kept a tight grip over the peasants, resulting in the arrest and imprisonment of the leader of the Agrarian Union, Aleksandur Stamboliyski. The Russian Revolution of 1916 had a huge effect on the Bulgarian population, with antiwar and anti-monarchy feelings spreading across both the soldiers and the workers of cities.
With the collapse of Russia and Austria-Hungary reeling, the Romanians joined the war and headed straight for Sofia. At the same time Greek forces finally broke through the trenches and marched across southern Bulgaria. Radoslavov's government resigned, and an armistice was signed.
Stamboliyski was released from prison and became the new Prime Minister. He favored reforms over a revolution disbanding the monarchy. Stamboliyski convinced Tsar Ferdinand to step down to be replaced by his son Boris, in order to calm the democratic revolutionaries. The rest of the revolutionaries were suppressed by the army and the police. In 1918, the Treaty of Munich was signed, which forced the disbandment of the Bulgarian army. Bulgaria's Aegean coastline was lost to Greece, along with the majority of its Macedonian territory. There was also territorial concessions to Romania. These lost territories nearly shattered the dream of establishing a state for all Bulgarians in the Balkans, resulting in the establishment of the Internal Macedonian Revolutionary Organization (IMRO), which favored war to regain Bulgaria's territory.