quality:correction
History

In antiquity, the Roman Empire brought about integration of multiple European and Mediterranean territories. The numerous subsequent claims of succession of the Roman Empire, even the iterations of the Classical Empire and its ancient peoples, have occasionally been reinterpreted in the light of post-1950 European integration as providing inspiration and historical precedents. Important examples include the Holy Roman Empire, the Hanseatic League, the Peace of Westphalia, the Napoleonic Empire, and the unification of Germany, Italy, and the Balkans as well as the Latin Monetary Union.

Following the catastrophe of the First World War of 1914–1918, thinkers and visionaries from a range of political traditions again began to float the idea of a politically unified Europe. In the early 1920s a range of international organisations were founded (or re-founded) to help like-minded political parties to coordinate their activities. These ranged from the Comintern (1919), to the Labour and Socialist International (1921) to the Radical and Democratic Entente of centre-left progressive parties (1924), to the Green International of farmers' parties (1923), to the centre-right International Secretariat of Democratic Parties inspired by Christianity (1925). While the remit of these international bodies was global, the predominance of political parties from Europe meant that they facilitated interaction between the adherents of a given ideology across European borders. Within each political tradition, voices emerged advocating not merely the cooperation of various national parties, but the pursuit of political institutions at the European level.

One of the first to articulate this view was Richard von Coudenhove-Kalergi, who outlined a conservative vision of European unity in his Pan-Europa manifesto (1923). The First Paneuropean Congress took place in Vienna in 1926, and the association possessed 8000 members by the time of the 1929 Wall Street Crash. They envisaged a specifically Christian, and by implication Catholic, Europe. The British civil-servant and future Conservative minister Arthur Salter published a book advocating The United States of Europe in 1933.

In contrast the Soviet commissar (minister) Leon Trotsky raised the slogan "For a Soviet United States of Europe" in 1923, advocating a Europe united along communist principles.

Among liberal-democratic parties, the French centre-left undertook several initiatives to group like-minded parties from the European states. In 1927, the French mathematician and politician Émile Borel, a leader of the centre-left Radical Party and the founder of the Radical International, set up a French Committee for European Cooperation, and a further twenty countries set up equivalent committees. However, it remained an élite venture: the largest committee, the French one, possessed fewer than six-hundred members, two-thirds of them parliamentarians. Two centre-left French prime ministers went further. In 1929 Aristide Briand gave a speech in the presence of the League of Nations Assembly in which he proposed the idea of a federation of European nations based on solidarity and in the pursuit of economic prosperity and political and social co-operation. In 1930, at the League's request, Briand presented a Memorandum on the organisation of a system of European Federal Union. The next year the future French prime minister Édouard Herriot published his book The United States of Europe. Indeed, a template for such a system already existed, in the form of the 1921 Belgian and Luxembourgish customs and monetary union.

Support for the proposals by the French centre-left came from a range of prestigious figures. Many eminent economists, aware that the economic race-to-the-bottom between states was creating ever-greater instability, supported the view: these included John Maynard Keynes. The French political scientist and economist Bertrand Jouvenel remembered a widespread mood after 1924 calling for a "harmonisation of national interests along the lines of European union, for the purpose of common prosperity". The Spanish philosopher and politician, Ortega y Gasset, expressed a position shared by many within Republican Spain: "European unity is no fantasy, but reality itself; and the fantasy is precisely the opposite: the belief that France, Germany, Italy or Spain are substantive & independent realities." Eleftherios Venizelos, Prime Minister of Greece, outlined his government's support in a 1929 speech by saying that "the United States of Europe will represent, even without Russia, a power strong enough to advance, up to a satisfactory point, the prosperity of the other continents as well".

Between the two world wars, the Polish statesman Józef Piłsudski (1867–1935) envisaged the idea of a European federation that he called Międzymorze ("Intersea" or "Between-seas"), known in English as Intermarium, which was a Polish-oriented version of Mitteleuropa.

The Great Depression, the rise of fascism and communism and subsequently World War II prevented the inter-war movements from gaining further support: between 1933 and 1936 most of Europe's remaining democracies became dictatorships, and Ortega's Spain and Venizelos's Greece had both plunged into civil war. But although the social-democratic, liberal or Christian-democratic supporters of European unity were out of power during the 1930s and unable to put their ideas into practice, many would find themselves in power in the 1940s and 1950s, and better-placed to put into effect their earlier remedies against economic and political crisis.

During World War II (1939–1945) Nazi Germany came to dominate - directly or indirectly - much of Europe at various times. The plans for German-oriented political, social, and economic integration of Europe - such as the New Order, the Greater Germanic Reich and Generalplan Ost - did not survive the war.

At the end of World War II, the continental political climate favoured unity in democratic European countries, seen by many as an escape from the extreme forms of nationalism which had devastated the continent. In a speech delivered on 19 September 1946 at the University of Zürich in Switzerland, Winston Churchill postulated a United States of Europe. The same speech however contains remarks, less-often quoted, which make it clear that Churchill did not initially see Britain as being part of this United States of Europe:

We British have our own Commonwealth of Nations... And why should there not be a European group which could give a sense of enlarged patriotism and common citizenship to the distracted peoples of this turbulent and mighty continent and why should it not take its rightful place with other great groupings in shaping the destinies of men?... France and Germany must take the lead together. Great Britain, the British Commonwealth of Nations, mighty America and I trust Soviet Russia—for then indeed all would be well—must be the friends and sponsors of the new Europe and must champion its right to live and shine.

We must build a kind of United States of Europe. In this way only, will hundreds of millions of toilers be able to regain the simple joys and hopes which make life worth living.