After WWII there was a movement (I don't know how big it was) for democratic nations on both sides of the Atlantic to federate under a federal constitution.
A book was written about it by Clarence Streit 'Union Now' both in 1939 and updated in 1949 and can be found in full online.
http://www.constitution.org/aun/aun0--00.htmStreit argued that several nations should federate and went as far as to write a draft consitution and nominated founding members.
In his 1939 edition his founders list included:
US
Canada
UK
France
Holland
Belgium
Denmark
Norway
Australia
New Zealand
South Africa
Ireland
Switzerland
Sweden
Finland.
In his 1949 edition Streit suggested that NATO founding members be the nucleus of this union.
The idea has its day in the 1950's and 1960's when the idea of an Atlantic convention was mooted by some in the US Congress and a North American confederation was a mooted by both Nixon and Rockefeller in their 1960 deal for Nixon to ascend to the GOP presidential nomination of that year.
But now the idea is dust. Why did this happen ?
and
If the Atlantic union came into being what would it be like?
What would have happened to the cold war?
What would an Atlantic Union election look like?