I'm about 20 pages from the end of Kershaw's biography of Hitler. A book I'd recommend, but it is long. In discussing the events of 1940, Kershaw wrote that Hitler wanted to either quickly finish off Britain or make peace with it, because he was worried that the USA would come into the war on Britain's side.
My question is, why was he sure that if the USA entered, it would be on Britain's side?
I think with hindsight, America likes to depict itself as the saviour of Europe and defender of the minorities of Europe and that this was inevitable, but in 1940 there were plenty of isolationists in the USA, more Americans had German roots than British roots, American business had been eager to deal with the Nazis, and it was still recovering from the depression. So why was Hitler so sure it would enter at all and on the side of Britain if it did? Was FDR's pro-interventionist stance clear at this point (mid-1940) and was it necessarily obvious that he could drag a reluctant USA with him?