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.

Development of Europe as a region

Europe as a continent 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.

In ancient Greek geography, the known world was divided into three major landmasses—Europe, Asia, and Libya—helping establish Europe as one of the world’s principal continents.

Roman Europes 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 ecumene, 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 legitimize their rule over larger areas of Europe, though not exclusively.

Other Europes 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.

Ideas of European unity before 1948

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.

In 15th century, King of Bohemia George of Poděbrady proposed the Treaty on the Establishment of Peace throughout Christendom which sought to end military conflict between Christian kingdoms of Europe. The treaty proposed a multilateral framework, including a peaceful dispute resolution process, but despite a vigorous promotional campaign, the proposal was ultimately unsuccessful. This effort has been occasionally noted as a first coherent proposal for a proto-European Union.

In the Congress of Aix-la-Chapelle of 1818, Tsar Alexander, as the most advanced internationalist of the day, suggested a kind of permanent European union and even proposed the maintenance of international military forces to provide recognised states with support against changes by violence.

Pan-European political thought truly emerged during the 19th century, inspired by the liberal ideas of the French and American Revolutions. The following Napoleonic Wars and First French Empire (1804–1815), brought down the Holy Roman Empire, enabled nationalism and following the Congress of Vienna, the ideals of internationalism like with Immanuel Kant and European unity flourished across the continent, especially in the writings of Wojciech Jastrzębowski (1799–1882) or Giuseppe Mazzini (1805–1872). The term United States of Europe () was used at that time by Victor Hugo (1802–1885) during a speech at the International Peace Congress held in Paris in 1849:

From World War I to World War II

During the interwar period, the consciousness that national markets in Europe were interdependent though confrontational, along with the observation of a larger and growing US market on the other side of the ocean, nourished the urge for the economic integration of the continent. In 1920, advocating the creation of a European economic union, the British economist John Maynard Keynes wrote that "a Free Trade Union should be established ... to impose no protectionist tariffs whatever against the produce of other members of the Union."John Maynard Keynes, Economic Consequences of the Peace, New York: Harcourt, Brace & Howe, 1920, pp. 265–66. During the same decade, the Austrian Richard von Coudenhove-Kalergi, in light of the dissolution of the Habsburg Empire, imagined as one of the first modern political unions of Europe, founded the Pan-Europa Movement. His ideas influenced his contemporaries, among whom was then-Prime Minister of France Aristide Briand. As French prime minister, Nobel Peace Prize laureate for the Locarno Treaties and follower of the Paneuropean Union Aristide Briand delivered a widely recognized speech at the League of Nations, the precursor of the United Nations, in Geneva on 5 September 1929 for a federal Europe to secure Europe and settle the historic Franco-German enmity.

World War II (1939–1945)

World War II from 1939 to 1945 demonstrated more than ever the horrors of war, but particularly also of extremism, of discrimination and of genocide. As with devastating wars before, there was a desire to ensure it could never happen again, particularly with the war bringing the world nuclear weapons. Most European countries failed to maintain their Great Power status, with the exception of the Soviet Union, which became a superpower after World War II and maintained that status for 45 years. This left two rival ideologically opposed superpowers.Europe in ruins in the aftermath of the Second World War ena.lu

With large scale war being waged in Europe once again in the 1930s and becoming World War II, the question of what to fight against and what for, had to be agreed on. A first agreement was the Declaration of St James's Palace of 1941, when Europe's resistance gathered in London. This was expanded on by the 1941 Atlantic Charter, establishing the Allies and their common goals, inciting a new wave of global international institutions like the United Nations (founded 1945) or the Bretton Woods System (1944).

During the 1943 Moscow Conference and Tehran Conference plans to establish joint institutions for a post-war world and Europe became increasingly an agenda. This led to a decision at the Yalta Conference in 1944 to form a European Advisory Commission, later replaced by the Council of Foreign Ministers and the Allied Control Council, following the German surrender and the Potsdam Agreement in 1945.

With war still raging, resistance movements formulated their vision of a post-war Europe, the Ventotene prison Manifesto of 1941 by Altiero Spinelli propagated European integration through the Italian Resistance and after 1943 through the Italian European Federalist Movement. In March 1943, in a radio address, the United Kingdom's leader Sir Winston Churchill spoke warmly of "restoring the true greatness of Europe" once victory had been achieved, and mused on the post-war creation of a "Council of Europe" which would bring the European nations together to build peace.

Aftermath (1945–1948)