Why did the United States adopt a policy of neutrality from 1914 to 1917?

The US policy of neutrality with regard to European disputes was not an innovation in 1914. Since George Washington, it had been the policy of the USA not to participate in European wars. From the Monroe Administration onward, the USA also held to a policy of precluding the intervention of non-American powers in hemispheric affairs. This policy had been strengthened by McKinley’s expulsion of Spain as an American power in the Spanish-American War, the Roosevelt Corollary, and Taft’s embrace of dollar diplomacy. It was not therefore surprising that the USA declined initially to be involved in a fratricidal conflict in Europe. After all, the policy of the United States had been to prevent intervention by Europe in their own Civil War, and immediately after in Mexico. On those odd occasions where the USA had been involved in world affairs, such as the negotiations between Russia and Japan to end their war in 1905, it had been as a neutral peacemaker.
In the two decades before 1914, Americans had also grown used to thinking about foreign policy as a Pacific or hemispheric affair. The great achievements and adventures of the country were focussed on Cuba, Mexico Venezuela, the Panama Canal, and the Philippines. In addition, the three largest ethnic groups in America, after those of British heritage, were German, Irish and Italian. New York City was the largest German city outside of Berlin and Vienna, and it was said by contemporaries that one could walk from Texas via Ohio to the Great Lakes speaking German. Since the Civil War, elections had typically been close and parties were fissile. It is hard to see, in 1914, President Wilson being confident of re-election, given that Theodore Roosevelt’s Progressives had in any event colonised the political space for war and that Republicans would oppose him.
It is also hard to see how America could have intervened in 1914-17. The Entente powers, for instance, were very close in terms of leadership (Asquith spoke French to Foch and Joffre, for example) and yet they were not fully coordinated. It is difficult to see how US land forces could have been deployed under US command in North West Europe, or in Turkey, or on the Eastern front. America did have the Great White Fleet, but even as it returned from circumnavigating in 1909 it had been rendered obsolete by the Dreadnought.  In any event, naval power was not decisive in Europe—the one battle was Jutland, which was inconclusive—and at least with neutrality the Germans might have been expected to restrain attacks on US shipping, if not stop them completely.
American banks and stock markets actually won out from neutrality. With each sale of gold or issue of war bonds, and with the pound off gold, the prospect arose of US surpluses being used to draw the leading economic power of the earth into debt and thence to supplant it. This was in fact what happened. British war loans essentially liquidated British wealth, in contrast to the US Liberty Bond issue of 1917, which represented investment by banks. At the same time, ongoing war allowed the massive investment of the UK and France in American stock markets to be sold and to pass into American hands.  War was good for the American financial industry, which was coordinated through the newly established Federal Reserve but which was also represented by powerful figures of vast wealth on the US scene, such as J.P.Morgan Jnr. Morgan stretched out huge lines of credit to France and Russia, and only supported US intervention when it looked as though those powers were in trouble in 1916. Morgan’s perceived influence over 2200 American banks, which were earning 1% commission from UK arms purchases as well as offering secured and unsecured loans to all three Entente powers, was such that he was shot in 1915 in an attempt by an activist to stop arms sales to the conflict. He survived to manage German reparations and British loan repayments in 1919.

Serious political opposition also existed to the idea of American intervention in the Great War. The early part of the twentieth century was the high point of US Socialism. Though there were only two socialist congressmen, Eugene Debs had received a significant 6% of the presidential vote in 1912, and over 70 Mayors represented the urban Socialist interest. Socialism in New England and the Mid-West was a concentrated vote, and was anti-war. In addition, the Womens’ Movement was rising in urban and Western settings, mixing prohibitionist idealism with the campaign for federal suffrage. It was a movement that could already command votes and support in many State legislatures and ballots (and therefore in the Senate, which was opened but not wholly converted to popular election from 1912). The Womens’ Peace Party was particularly prominent in this regard, and employed direct action tactics. In an earlier guise (the WPP grew out of other groups in 1915 and changed name again after that year) it had introduced the tactic of ‘political demonstrations’ which merged parades with protest to American life.  An American Union Against Militarism had also emerged by 1915, and, bizarrely, this ran parallel to the activities of moguls such as Andrew Carnegie and Henry Ford to keep America out of war. I write ‘bizarre’ since the AUAM ended up a Soviet organisation.

A final point to note is that Woodrow Wilson almost lost in 1916. He did in fact retire to bed on the night of the results believing that he had lost. This belief was so sure that he contemplated appointing his opponent Secretary of State and then resigning along with the Vice-president to allow for a swift handover of power on the then-existing rules.  Wilson’s eventual victory was delivered with a very small popular vote margin of 600,000, and could easily have been lost in several key states. The win was attributed to neutrality under the slogan ‘He Kept Us Out Of War’. Wilson had even lost votes for intervening in Mexico’s Civil War, though he used the issue during the campaign to suggest Mexican issues would cause even worse grief if allied to German hostility. In that context, his 1917 Inaugural address, a month before intervention, was a clarion call for peace—and for neutrality. Even at that late hour, it would take active German efforts to sink ships, inflame sentiment, and avoid peace, as well as considerable British and financial pressure, before the American people were decided for War.