Michael the Brave in the context of "Principality of Transylvania (1570–1711)"

Wallachia is a geographical region of modern-day Romania, as well as one of the two historical Romanian principalities that laid the foundation for the establishment of the modern Romanian state. It is situated north of the Lower Danube and south of the Southern Carpathians. Wallachia was traditionally divided into two sections, Muntenia (Greater Wallachia) and Oltenia (Lesser Wallachia). Dobruja could sometimes be considered a third section due to its proximity and brief rule over it. Wallachia as a whole is sometimes referred to as Muntenia through identification with the larger of the two traditional sections.

Wallachia began to form as a principality around the 13th century, following the gradual unification of several smaller Romanian political entities. By 1330, the state had consolidated following Basarab I's victory in the Battle of Posada against the Kingdom of Hungary, ushering in a period of relative independence. In 1417, Wallachia was forced to accept the suzerainty of the Ottoman Empire for the first time; this suzerainty lasted until the mid-19th century. However in general Wallachia was able to preserve autonomy within the Empire as well as experience interruptions to Ottoman rule brought about by local rulers such as Vlad the Impaler and Michael the Brave and later external powers such as the Polish-Lithuanian Commonwealth and the Russian Empire.

In Romanian historiography, the Great Union (Romanian: Marea Unire) or Great Union of 1918 (Marea Unire din 1918) was the series of political unifications the Kingdom of Romania had with several of the Romanian historical regions, starting with Bessarabia on 27 March 1918, continuing with Bukovina on 28 November 1918 and finalizing with Transylvania (on its broad meaning) on 1 December 1918 with the declaration of the union of this region with Romania during an assembly at the city of Alba Iulia. Romanians also consider several other events as preludes to the Great Union, such as the unification of Moldavia and Wallachia (also known as the Little Union, Mica Unire) in 1859 or the independence of the country and the annexation of Northern Dobruja in 1878, and also the occupation of Transylvania and Moldavia by the Prince of Wallachia, Michael the Brave, in 1600.

Today, the Great Union has an important meaning in Romania, and it is commemorated in the Great Union Day, the national day of the country, every 1 December. The centenary of the Great Union on 1 December 2018 was widely celebrated in Romania, with military parades at cities like Alba Iulia and Bucharest to which many people (up to 550,000, 100,000 of them in Alba Iulia alone), including the President of Romania Klaus Iohannis, attended. The centenary was also celebrated in Moldova, where more than 100 localities and 3 districts declared unification with Romania.

The Middle Ages in Romania began shortly after the withdrawal of the Roman legions from the former Roman province of Dacia in the late 3rd century and with the start of the Early Middle Ages and the Migration Period that followed afterwards respectively. It subsequently came to an end with the reign of Domn Michael the Brave (1593–1601) who managed, for a short time between 1599 and 1600, to rule Wallachia, Moldavia, and Transylvania together, the three principalities whose territories were to be united some three centuries later to form modern and contemporary Romania.

Over most of this period, Banat, Crișana, Maramureș, and Transylvania – now regions in Romania to the west of the Carpathian Mountains – were part of the Kingdom of Hungary. They were divided into several types of administrative units, such as "counties" and "seats". The heads of the Transylvanian counties or "counts" were subordinated to a special royal official called voivode, but the province was seldom treated as a single unit, since the Székely and Saxon seats were administered separately. In the kingdom, Romanian peasants, being Orthodox, were exempt from the tithe, an ecclesiastical tax payable by all Roman Catholic commoners. However, Romanian noblemen slowly lost the ability to participate in political life, as the 14th-century monarchs pursued a zealous pro-Catholic policy. Their position became even worse after 1437 when the so-called "Union of Three Nations", an alliance of the Hungarian noblemen, the Székelys, and the Saxons, was formed in order to crush the Bobâlna peasant uprising.

The Battle of Șelimbăr, or Battle of Sellenberk (Hungarian: Sellenberk; German: Schellenberg), took place on 18 October 1599 between the Wallachian army of Michael the Brave (Romanian: Mihai Viteazul) and the Transylvanian-Hungarian army of Andrew Báthory (Hungarian: Báthory András). The battle was fought near the village of Șelimbăr (Hungarian: Sellenberk) close to Sibiu (German: Hermannstadt; Hungarian: Nagyszeben).