Northern Dobruja in the context of "Great Union"

The Odrysian kingdom (/oʊˈdrɪʒən/; Ancient Greek: Βασίλειον Ὀδρυσῶν), also known as Odrysia, was an ancient Thracian state that thrived between the early 5th century BC and the early 3rd / late 1st century BC. Located in present-day Bulgaria, southeastern Romania (Northern Dobruja), northern Greece and European Turkey, it was a tribal amalgam dominated by the Odrysians that was the first large political entity to develop in the eastern Balkans.

The Odrysian kingdom was founded by king Teres I, who was exploiting the collapse of the Persian presence in Europe due to the failed invasion of Greece in 480–79. Teres and his son Sitalces pursued a policy of expansion, making the kingdom one of the most powerful of its time. Throughout much of its early history it remained an ally of Athens and even joined the Peloponnesian War on its side. By 400 BC the state showed first signs of fatigue, although the skilled Cotys I initiated a brief renaissance that lasted until his murder in 360 BC.

The Kingdom of Romania (Romanian: Regatul României) was a constitutional monarchy that existed from 25 March [O.S. 13 March] 1881 with the crowning of prince Karl of Hohenzollern-Sigmaringen as King Carol I (thus beginning the Romanian royal family), until 1947 with the abdication of King Michael I and the Romanian parliament's proclamation of the Romanian People's Republic.

From 1859 to 1877, Romania evolved from a personal union of two principalities: (Moldavia and Wallachia) called the Unification of Moldavia and Wallachia also known as "The Little Union" under a single prince to an autonomous principality with a Hohenzollern monarchy. The country gained its independence from the Ottoman Empire during the 1877–1878 Russo-Turkish War (known locally as the Romanian War of Independence), after which it was forced to cede the southern part of Bessarabia in exchange for Northern Dobruja. The kingdom's territory during the reign of King Carol I, between 13 (O.S.) / 25 March 1881 and 27 September (O.S.) / 10 October 1914 is sometimes referred to as the Romanian Old Kingdom, to distinguish it from "Greater Romania", which included the provinces that became part of the state after World War I (Bessarabia, Banat, Bukovina, and Transylvania).

Dobruja or Dobrudja (US: /ˈdoʊbrʊdʒə/; Bulgarian: Добруджа, romanized: Dobrudzha or Dobrudža; Romanian: Dobrogea, pronounced [ˈdobrodʒe̯a] or [doˈbrodʒe̯a]; Turkish: Dobruca; Ukrainian and Russian: Добруджа, romanized: Dobrudzha) is a geographical and historical region in Southeastern Europe that has been divided since the 19th century between the territories of Bulgaria and Romania. It is situated between the lower Danube River and the Black Sea, and includes the Danube Delta, the Romanian coast, and the northernmost part of the Bulgarian coast. The territory of Dobruja is made up of Northern Dobruja, which is a part of Romania, and Southern Dobruja, which is a part of Bulgaria.

The territory of the Romanian region Dobrogea is organised as the counties of Constanța and Tulcea, with a combined area of 15,588 km (6,019 sq mi) and, as of 2021, a population of slightly less than 850,000. Its main cities are Constanța, Tulcea, Medgidia, and Mangalia. Dobrogea is represented by dolphins in the coat of arms of Romania.

The Romanian Old Kingdom (Romanian: Vechiul Regat or just Regat; German: Regat or Altreich) is a colloquial term referring to the territory covered by the first independent Romanian nation state, which was composed of the Romanian Principalities: Wallachia and Moldavia. The union of the two principalities was achieved when, under the auspices of the Treaty of Paris (1856), the ad hoc Divans of both countries, which were then under Ottoman Empire suzerainty, voted for Alexander Ioan Cuza as their prince. This process achieved a de facto unification under the name of the United Principalities of Moldavia and Wallachia. The region itself is defined by the result of that political act, followed by the Romanian War of Independence, the inclusion of Northern Dobruja and the transfer of the southern part of Bessarabia to the Russian Empire in 1878, the proclamation of the Kingdom of Romania in 1881, and the annexation of Southern Dobruja in 1913.

The term came into use after World War I, when the Old Kingdom became Greater Romania, after including Transylvania, Banat, Bessarabia, and Bukovina. The term now has mainly a historical relevance and is otherwise used as a common term for all regions in Romania included in both the Old Kingdom and the present borders (Wallachia, Moldavia, and Northern Dobruja).

Moesia (/ˈmiːʃə, -siə, -ʒə/; Latin: Moesia; Greek: Μοισία, romanized: Moisía) was a Roman province situated in the Balkans south of the Danube River. Created after the Danubian-Balkan conquest during the reign of Augustus, Moesia included most of the territory of modern eastern Serbia, Kosovo, north-eastern Albania, northern parts of North Macedonia (Moesia Superior), Northern Bulgaria, Romanian Dobruja and small parts of Southern Ukraine (Moesia Inferior).

The Aromanians (Aromanian: Armãnji, Rrãmãnji) are an ethnic group native to the southern Balkans who speak Aromanian, an Eastern Romance language. They traditionally live in central and southern Albania, south-western Bulgaria, northern and central Greece, and North Macedonia, and can currently be found in central and southern Albania, south-western Bulgaria, south-western and eastern North Macedonia, northern and central Greece, southern Serbia, and south-eastern Romania (Northern Dobruja). An Aromanian diaspora living outside these places also exists. The Aromanians are known by several other names, such as "Vlachs" or "Macedo-Romanians" (sometimes used to also refer to the Megleno-Romanians).

The term "Vlachs" is used in Greece and in other countries to refer to the Aromanians, with this term having been more widespread in the past to refer to all Romance-speaking peoples of the Balkan Peninsula and Carpathian Mountains region (Southeast Europe).