The Kingdom of Bulgaria or the Tsardom of Bulgaria (Bulgarian: Царство България, Tsarstvo Balgariya; also called Third Bulgarian Tsardom to distinguish it from the First Bulgarian Tsardom and the Second Bulgarian Tsardom) was a constitutional monarchy, created on 22 September 1908 (old style), as а result of an elevation of the Bulgarian state to independendent kingdom from tributary principality. This move was taken by Ferdinand who was crowned a Tsar at the declaration of independence, mainly taken for military plans and more accurately for seeking options for unification of all lands in the Balkans populated with ethnic Bulgarian majority, seized from Bulgaria and given to the Ottoman Empire with the Treaty of Berlin. The state itself was one of the most actively warring as a proportion of its existence for which was referred to as "the Balkan Prussia", for several years Bulgaria mobilized army of more than 1 million people from its population of about 5 million and in the next decade (1910-20) it engaged in three wars - the First, the Second Balkan War and the First World War, but lost both the Balkan and the World War. After this the Bulgarian army was forbidden to exist by the winning side of the World War and was actually dibanded and all plans for national unification of the Bulgarian lands failed. After less than two decades Bulgaria was again warring for national unification in the Second World War, but was fighting again on the losing side, which was a fourth lost war. In 1946, the monarchy was abolished, its final Tsar was sent into exile and the Kingdom was replaced by a People's Republic. Although rarely, it is sometimes referred to as the Third Bulgarian Empire, as in the Middle Ages the term Tsardom meant an Empire. However, the Third Bulgarian state was internationally recognized as a Kingdom.

Coordinates: 42°45′N 25°30′E / 42.75°N 25.5°E / 42.75; 25.5

Bulgaria ⁱ/bʌlˈɡɛəriə/ (Bulgarian: България, IPA: [bɤ̞ɫˈɡarijɐ]), is a country located in Southeastern Europe. It is bordered by Romania to the north, Serbia and the Macedonia to the west, Greece and Turkey to the south and the Black Sea to the east. With a territory of 110,994 square kilometres (42,855 sq mi), Bulgaria is Europe's 14th-largest country. Its location has made it a historical crossroad for various civilisations and as such it is the home of some of the earliest metalworking, religious and other cultural artifacts in the world.

Prehistoric cultures began developing on Bulgarian lands during the Neolithic period. Its ancient history was marked by the presence of the Thracians, and later by the Greeks and Romans. The emergence of a unified Bulgarian ethnicity and state dates back to the First Bulgarian Empire, which dominated most of the Balkans and functioned as a cultural hub for Slavic peoples during the Middle Ages. With the downfall of the Second Bulgarian Empire in 1396, its territories came under Ottoman rule for nearly five hundred years. The Russo-Turkish War of 1877–1878 resulted in the Third Bulgarian State, recognised in 1908. The following years saw several conflicts with its neighbours, which prompted Bulgaria to align with Germany in both World Wars. In 1946 it became a Communist republic with a single-party system until 1989, when the Communist Party allowed multi-party elections. After 1990 Bulgaria transitioned to democracy and a market-based economy.

Boris III the Unifier, Tsar of Bulgaria (30 January 1894 – 28 August 1943), originally Boris Klemens Robert Maria Pius Ludwig Stanislaus Xaver (Boris Clement Robert Mary Pius Louis Stanislaus Xavier), son of Ferdinand I, came to the throne in 1918 upon the abdication of his father, following the defeat of the Kingdom of Bulgaria during World War I. This was the country's second major defeat in only five years, after the disastrous Second Balkan War (1913). Under the Treaty of Neuilly, Bulgaria was forced to cede new territories and pay crippling reparations to its neighbours, thereby threatening political and economic stability. Two political forces, the Agrarian Union and the Communist Party, were calling for the overthrowing of the monarchy and the change of the government. It was in these circumstances that Boris succeeded to the throne.

Boris was born on 30 January 1894 in Sofia. He was the first son of Prince Ferdinand of Bulgaria and his wife Princess Marie Louise.

In February 1896 his father paved the way for the reconciliation of Bulgaria and Russia with the conversion of the infant Prince Boris from Roman Catholicism to Eastern Orthodox Christianity, a move that earned Ferdinand the frustration of his wife, the animosity of his Catholic Austrian relatives (particularly that of his uncle, Francis Joseph of Austria) and excommunication from the Catholic Church. In order to remedy this difficult situation Ferdinand christened all his remaining children as Catholics. Nicholas II of Russia stood as godfather to Boris and met the young boy during Ferdinand's official visit to Saint Petersburg in July 1898.