The first period to be analysed is that which saw the first entry of the United States on to the stage of world politics and its first great withdrawal. This period opens at the end of the Spanish–American war and with the Diamond Jubilee of Queen Victoria and ends with the failure of the United States Senate to ratify the Treaty of Versailles and with the emergence of Britain, crippled and impoverished, into the dubious light of victory over the Central Powers. In terms of the formal relations between Britain and the United States, the period divides itself into four main sections: the Anglo-American settlement of the major issues of conflict between the two countries between 1898 and 1905; the abortive Anglo- American arbitration treaty and conflicts over dollar diplomacy; American neutrality during the great European war; and finally the two years of co-belligerency.

Politics in the United States in this period were dominated by the rise of the Progressive movement, which, although divided in its loyalties between the Republican party, the Democrats and, in 1912, Theodore Roosevelt's breakaway Progressive party, imparted one and the same impetus to all three, an impetus the manifestations of which vary from party to party only with the entrenched strength of business, machine and states rights conservatives. In international affairs, by far the greatest number of the leading progressives were imperialist and expansionist in their attitudes during the first decade of the twentieth century, even such ‘irreconcilables’, in 1919 terms, as William Borah and Robert La Follette.