Unpublished papers in Britain's National Archives at Kew reveal curious undercurrents in Anglo-American relations. After the conclusion of the Boer War, for example, the British Army supposed that the next major conflict would be not with Germany but with the U.S. A memo printed for circulation in July 1904 entitled ‘A Study of the Strategical Considerations Affecting the Invasion of Canada by the United States' compared the potential military resources of Canada with those of the Confederacy in the Civil War of 1861-65, except that ‘she will not be cut off from the sea as was the South, an inestimable advantage.' A later General Staff paper emphasized ‘the incalculable importance of dominating Lake Ontario in the case of hostilities.'

A memo of January 1906 drew attention to the increasing size of the American Army, which had more than doubled in strength since 1898: ‘it is only reasonable to assume that these preparations have been made with a view to a possible conflict with Great Britain.' (WO 106/40) In November 1906 the British War Office issued an 83-page booklet on ‘The Military Geography of the Frontier Region of the United States.' It began with the suggestion that an invasion of the U.S. from Canada might be an option: ‘Although a war between Great Britain and the United States will in all probability take the shape of an invasion of Canada by the latter Power, the possibility of a counter attack from Canada must not be overlooked.'