The European Union is a geo-political entity, created in 1993, covering a large portion of the European continent. It is founded upon numerous treaties and has undergone expansions and secessions that have taken it from six member states to 27, a majority of the states in Europe.

Since the beginning of the institutionalised modern European integration in 1948, the development of the European Union has been based on a supranational foundation that would "make war unthinkable and materially impossible" and reinforce democracy amongst its members as laid out by Robert Schuman and other leaders in the Schuman Declaration (1950) and the Europe Declaration (1951). This principle was at the heart of the European Coal and Steel Community (ECSC) (1951), the Treaty of Paris (1951), and later the Treaty of Rome (1957) which established the European Economic Community (EEC) and the European Atomic Energy Community (EAEC). The Maastricht Treaty (1992) created the European Union with its pillars system, including foreign and home affairs alongside the European Communities. This in turn led to the creation of the single European currency, the euro (launched 1999). The ECSC expired in 2002. The Maastricht Treaty has been amended by the treaties of Amsterdam (1997), Nice (2001) and Lisbon (2007), the latter merging the three pillars into a single legal entity, though the EAEC has maintained a distinct legal identity despite sharing members and institutions.

The known world in Ancient Greece was differentiated into three landmasses: Asia, "Libya" (Africa) and Europe, giving rise to identifying the European landmass as a coherent area, a continent.

The European landmass was populated and territorialized by many long before its conceptualization as a coherent continent. But the Roman Empire, an empire built on the Hellenistic world and Alexandrian Empire, Ancient Egypt, the Levant and North Africa, became the first state to control the whole Mediterranean Basin and also large parts, particularly the Southern and Western parts of the European landmass. This historic prominence in the Mediterranean Basin and Europe has been invoked by states that came after it, claiming succession to Roman authority and to legitimate their rule over lands throughout the former Roman eucomene, and therefore also in Europe, particularly in Western Europe, the lands of the later Western Roman Empire of Latin Rome. The latter established Western Europe as a coherent and independent political area of Europe, which has taken sometimes prominence, as simply the West, over the concept of Europe. Similarly other concepts for Europe as a coherent political space have been used, such as for example Frangistan.

The claims for the succession of the control over the West, after the fall of Western Rome in 476 developed into the concept of translatio imperii ("transfer of rule") through the King of Italy, enabling claims by the Goths, Lombards, Frankish Empire (481/800–843) and Holy Roman Empire (800/962–1806). Furthermore, during and after the Roman Empire the concept renovatio imperii ("restoration of the empire") was employed, particularly in the forms of the religiously inspired Imperium Christianum ("christian empire"), and later the Reichsidee ("imperial idea"), to establish and sustain a coherent political region. As such the position and extent of influence of the Papacy over a range of European lands has been a force, while not exclusively European, capable of rallying European powers under a common Christian identity. That said, some European powers, such as France (after the installment of the Holy Roman Empire with East Francia) and the Polish-Lithuanian Commonwealth challenged the Western Roman authority through the Western Schism and the Italian Wars, while England, the Dutch Republic, Prussia, the Swedish Empire and Denmark–Norway also challenged the Papal one with Protestant Reformation.

The Greek Eastern Rome, also called Byzantine Empire, remained long after the dissolution of the Western Roman Empire, sustaining a coherent political space also over large areas of Europe, particularly of (South-) Eastern Europe, or simply the East, giving rise to the other major particular Europe. With the fall of the Eastern Roman Empire in 1453, the Ottoman Empire and the Russian Tsardom, and ultimately the Empire (1547–1917), with Moscow as the so-called Third Rome, used claims of inheritance of the eastern Roman Empire to legitimate their rule over larger areas of Europe, though not exclusively.

But also other polities of Europe have established, independently from Rome and Byzantine, their European realms, such as a range of pre-Roman or pre-Christian Greek, Germanic, Celtic, Slavic and Hungarian powers, Khanates, or Al-Andalus and the Sicilian Emirate.

Apart from the ideas of federation, confederation, or customs union such as Winston Churchill's 1946 call for a "United States of Europe", the original development of the European Union was based on a supranational foundation that would "make war unthinkable and materially impossible" A peaceful means of some consolidation of European territories used to be provided by dynastic unions; less common were country-level unions, such as the Polish–Lithuanian Commonwealth and Austro-Hungarian Empire.