What has been the idea of Atlanticism 
 Atlanticism, also known as Transatlanticism, is the ideological belief in support for a close relationship between the peoples and governments of the allies to NATO in Northern America (the United States and Canada) and those in Europe (the countries of the European Union, Ukraine, the United Kingdom, Switzerland, Norway, Iceland, etc.) on political, economic, and defense issues to the purpose of maintaining the security and prosperity of the participating countries and protect liberal democracy and the progressive values of an open society that unite them under multiculturalism. The term derives from the Atlantic Ocean, which is bordered by North America and Europe.

The term can be used in a more specific way to refer to support for North Atlantic military alliances against the Soviet Union, or in a more expansive way to imply broader cooperation, perceived deeply shared values, a merging of diplomatic cultures, as well as a sense of community and some degree of integration between North America and Europe. In practice, the philosophy of Atlanticism encourages active North American, particularly American, engagement in Europe and close cooperation between states on both sides of the ocean. Atlanticism manifested itself most strongly during the Second World War and in its aftermath, the Cold War, through the establishment of various Euro-Atlantic institutions, most importantly NATO and the Marshall Plan.

Atlanticism varies in strength from region to region and from country to country based on a variety of historical and cultural factors. It is often considered to be particularly strong in Eastern Europe, Central Europe, Ireland and the United Kingdom (linked to the Special Relationship). Politically, it has tended to be associated most heavily and enthusiastically but not exclusively with classical liberals or the political right in Europe. Atlanticism often implies an affinity for U.S. political or social culture, or affinity for Europe in North America, as well as the historical bonds between the two continents.

There is some tension between Atlanticism and continentalism on both sides of the Atlantic, with some people emphasising increased regional cooperation or integration over trans-Atlantic cooperation. The relationship between Atlanticism and North American or European integrations is complex, and they are not seen in direct opposition to one another by many commentators. Internationalism is the foreign policy belief combining both Atlanticism and continentalism.