From 1917: War, Peace, and Revolution, by David Stevenson (OUP Oxford, 2017), Kindle pp. 38-39:
In 1910 out of a US population of 92 million, 2.5 million were German-born and 5.8 million of the native-born had one or both German-born parents. Although Wilson believed 90 per cent of America’s people were strongly pro-Allied, he had grounds to fear that rival allegiances would breed civil strife.
The traditional corollary to political abstention was unimpeded commerce. Exporting to belligerents was unobjectionable, the more so as America was in recession and the fighting expected to be brief. But demands for artillery, munitions, steel, machine tools, chemicals, and food and raw materials rose far higher than anticipated, fuelling one of the strongest upsurges in US history. In the winter of 1914–15 German-Americans backed a proposal in Congress to embargo arms exports, but Wilson prevented the move as ‘a foolish one, as it would restrict our plants’. Commerce secretary, William Cox Redfield, and the Treasury secretary, William Gibbs McAdoo, urged the boom must be sustained, Redfield advising that exports were at record levels, and McAdoo using the extra revenue to pay off debt. Between 1915 and 1917 exports to Britain, Canada, France, Italy, and Russia grew from $3,445 million to $9,796 million (184 per cent); those of wheat by 683 per cent; and of copper by 277 per cent; but whereas pre-war trade with the Central Powers had been one-fifth of that with the Allies, now it shrank to 1 per cent. The Allies could find the shipping to transport their purchases and the cash or credit to pay for them; the Central Powers could find neither, so whatever stance America took would benefit one side. Britain had the world’s biggest merchant navy in 1914 (43 per cent of world tonnage—and the Allies in total 59 per cent, against the Central Powers’ 15 per cent). As the Allies converted to military production, however, they had less to export, and were less able to pay. The Wall Street banking giant, J. P. Morgan & Co., became the British government’s purchasing and financial agent and permitted it a growing overdraft, and in the summer of 1915 it advised the Allies to attempt a bond flotation. Following convention, Wilson had prohibited loans to belligerent governments. But McAdoo warned that ‘to maintain our prosperity we must finance it. Otherwise it may stop, and that would be disastrous.’ Finally Wilson approved the bond issue, and even if the primary motive was to sustain the boom and the yield proved disappointing, American policy had clearly altered to the Allies’ advantage. In 1915, 75 per cent of US exports went to the Allies or to countries that had broken relations with Germany and between 1913 and 1916 America’s percentage of French imports rose from 10 to 30. By 1916 bottlenecks on the railroads into New York stretched back for miles.