Despite its failure to join the League of Nations, the United States did not withdraw from international affairs in the 1920s. It participated in arms control negotiations; signed the Kellogg-Briand Pact, which outlawed war as an instrument of national policy but proved unenforceable; and expanded its foreign investments in Central and Latin America, Asia, the Middle East, and western Europe. In 1933 a new possibility for trade emerged when the Roosevelt administration extended diplomatic recognition to the Soviet Union (USSR).

Overall, the country did not retreat from foreign affairs so much as it refused to enter into collective security agreements that would restrain its freedom of action. To the extent that American leaders practiced isolationism, they did so mainly in the political sense of rejecting internationalist organizations such as the League of Nations, institutions that might require military cooperation to implement their decisions.

The experience of World War I had reinforced this brand of political isolationism, which was reflected in an outpouring of antiwar sentiments in the late 1920s and early 1930s. Best-selling novels like Ernest Hemingway’s Farewell to Arms (1929), Erich Maria Remarque’s All Quiet on the Western Front (1929), and Dalton Trumbo’s Johnny Got His Gun (1939) presented graphic depictions of the horror and futility of war. Beginning in 1934, Senate investigations chaired by Gerald Nye of North Dakota concluded that bankers and munitions makers—“merchants of death,” as one contemporary writer labeled them—had conspired to push the United States into war in 1917. Nye’s hearings appealed to popular antibusiness sentiment in Depression-era America.

Following the Nye Committee hearings, Congress passed a series of Neutrality Acts, each designed to make it more difficult for the United States to become entangled in European armed hostilities. In 1935 Congress prohibited the sale of munitions to either warring side and authorized the president to warn Americans against traveling on passenger liners of belligerent nations. The following year, lawmakers added private loans to the ban, and in 1937 they required belligerents to pay cash for nonmilitary purchases and ship them on their own vessels—so-called cash-and-carry provisions.

Events in Europe, however, made U.S. neutrality ever more difficult to maintain. After rising to power as chancellor of Germany in 1933, Adolf Hitler revived Germany’s economic and military strength despite the Great Depression. Hitler installed National Socialism (Nazism) at home and established the empire of the Third Reich abroad. The Führer (leader) whipped up patriotic fervor by scapegoating and persecuting Communists and Jews. To garner support for his actions, Hitler manipulated German feelings of humiliation for losing World War I and having been forced to sign the “war guilt” clause (see “Waging Peace” in chapter 20) and pointed to the disastrous effects of the country’s inflation-ridden economy. In 1936 Hitler sent troops to occupy the Rhineland between Germany and France in blatant violation of the Treaty of Versailles.

Hitler did not stop there. Citing the need for more space for the Germanic people to live, he pushed for German expansion into eastern Europe. In March 1938 he forced Austria to unite with Germany. In September of that year Hitler signed the Munich Accord with Great Britain and France, allowing Germany to annex the Sudetenland, the mainly German-speaking, western region of Czechoslovakia. Hitler still wanted more land and was convinced that his western European rivals would not stop him, so in March 1939 he sent German troops to invade and occupy the rest of Czechoslovakia. Hitler proved correct; Britain and France did nothing in response, a policy critics called appeasement.

Hitler’s Italian ally, Benito Mussolini, joined him in war and conquest. In 1935 Italian troops invaded Ethiopia. The following year, both Germany and Italy intervened in the Spanish civil war, providing military support for General Francisco Franco in his effort to overthrow the democratically elected, socialist republic of Spain. While the United States and Great Britain remained on the sidelines, only the Soviet Union officially assisted the Loyalist defenders of the Spanish republic. In violation of American law, private citizens, many of whom were Communists, volunteered to serve on the side of the Spanish Loyalists and fought on the battlefield as the Abraham Lincoln Brigade. Other sympathetic Americans, such as J. Robert Oppenheimer, provided financial assistance for the anti-Franco government. Despite these efforts, Franco’s forces seized control of Spain in early 1939, another victory for Hitler and Mussolini.