Secret US plan to attack UK in the 1930s

The United States and the United Kingdom have fought against each other a few times; during the War of Independence and the War of 1812.  But who would have thought that the two countries who have been allied to one another in the closing years of WW1, from 1941 during WW2 and have enjoyed a 'special relationship' for decades would have considered that war between them was a possibility in the 1930s?
Since the 19th century, military strategists in the United States had made plans for defending against attack by an external power, using colours associated with the US - blue and the British Empire - red.  During the cold war, the colours remained the same, but the proposed red enemy was the Soviet Union.
However, it certainly seems strange to us now that at a time of fascism and communism spreading across Europe, that the USA would draw up plans for a pre-emptive strike against the British.  But this is exactly what happened.
There were elements in the US government who saw the British Empire as a threat to US aspirations as a world power.  The British Empire had dealt with any potentially rising world powers with military intervention.
Along with a general anti-British feeling in the US, the American military drew up a plan to attack Canada and British interests in the Caribbean.  Military airfields were build along the Canadian border along with a significant build up of troops and military exercises.
It has been suggested that the initial attack planned on Nova Scotia would have meant a war on the eastern seaboard of the United States which would have included 6 million combatants. 
Both Churchill and Hitler saw this as a possibility.  Hitler wanted a British victory and would have allied with the UK against the US.
Imagine what the world would be like now if that had happened!