History of American Foreign Policy 101: The Interwar Period and World War II


To make sense of both the world of foreign policy and the world as it is, an understanding of United States foreign policy and its interaction with the policies of other nations is critical. It is the purpose of this series to give the reader an overview of the history of the United States' foreign policy, and show how it has helped shape the path of the United States and of international relations in general. Such illustration will include analyses of the United States' foreign policy in both theoretical assumptions and empirical application. The series will thus provide the reader with a foundation from which they will be able to accurately understand global historical events, and also critically examine and form opinions on the current and future United States' foreign policy.

This 101 series is divided into eight articles including:

  1. History of American Foreign Policy 101: Founding Principles

  2. History of American Foreign Policy 101: Looking West - The Monroe Doctrine and Manifest Destiny

  3. History of American Foreign Policy 101: The Beginnings of Empire and World War I

  4. History of American Foreign Policy 101: The Interwar Period and World War II

  5. History of American Foreign Policy 101: The Cold War: Confrontation and Containment

  6. History of American Foreign Policy 101: Cold War Part 2: Detente and Rapprochement

  7. History of American Foreign Policy 101: Unipolarity and the War on Terror

  8. History of American Foreign Policy 101: The Rise of China

This article will discuss the history of American foreign policy from the period of 1919 until 1945; from the end of the first world war to the end of the second. First, it will discuss the foreign policy of the United States in the immediate post world war I period, including its failure to join the League of Nations, and the re-entrenchment of isolationism in the 1920s. Next, it will examine America’s foreign policy in the years leading up to World War II, again focusing on its policy of neutrality and non-entangling alliances. Lastly, there will be an examination of America’s foreign policy in the Second World War, and how this policy led to an Allied victory, the ultimate ascension of the United States as the premier world power, and the foundation of the rules-based world order.

Dart, H. G. (1919). Uncle Sam Should’ve Stayed Home. [Cartoon]. Wikimedia Commons.

A Referendum on Isolation

After taking part in the negotiations of the Treaty of Versailles (1919), which would officially end World War I (1914-1919), Woodrow Wilson (1856-1921) returned home with the task of convincing two-thirds of the Senate to ratify the treaty. The ratification would also mean the approval of American entrance into the League of Nations, which was established by part I of the Versailles treaty (Magliveras, 1999). The League of Nations, the precursor to the United Nations, was an international body made up of sovereign member states which sought to avoid a repetition of the first World War through collective security, disarmament, free trade, and the peaceful settlement of international disputes (Covenant of the League of Nations). The theoretical origin of the League of Nations was in the dominant foreign policy circles at the time, specifically in America and Britain, which represented the ideas of ’liberal internationalism’ (Brown, 2019).

In its essence, the liberal diagnosis for the cause of the first world war was twofold. The first cause was domestic politics; that “war comes about because the people are led into it by militarists or autocrats, or because their legitimate aspirations to nationhood are blocked by undemocratic, multinational, imperial systems“ (Brown, 2019). The treaty of Versailles sought to address this by promoting liberal democratic political systems, in addition to the principle of self-determination. The second cause of the war, according to the liberals, was the nature of the international system: war and conflict arise due to the existence of “an international system without central authority”, meaning that states must guarantee their own survival through the preservation and improvement of their power, of which war is the final tool (Anderson, 2017). The League of Nations strove to address this second cause, the primary problem at the heart of international relations theory, that of the anarchic international system. In this sense, the League was to act as the missing central authority in the international system, one which would “provide public assurances of security backed by the collective will of all nations“ (Brown, 2019, p. 22).

Despite its idealistic aspirations, the League of Nations would become the greatest stumbling block to American ratification of the Treaty of Versailles, which would fall flat in the Senate. In fact, neither the general public nor the elite supported entrance into an international organisation which could jeopardise American sovereignty (Anderson, 2017). Moreover, the international Open Door policy supported by the League, which would lower tariffs and other barriers to free trade, did not appeal to Americans at the time. The American economy was already buzzing after the massive buildup of the industry during World War I, and with its abundant natural resources and massive internal market, it seemed that the promotion of free trade and the lowering of traditionally high American tariffs were both unnecessary and unwise (Anderson, 2017). Both of these factors would play heavily in the defeat of the Treaty of Versailles in the Senate in November of 1919.

(n.d.). (1929). A solemn crowd gathers outside the Stock Exchange after the crash. [Photograph]. Wikimedia Commons.

The defeat of the Treaty of Versailles would mark the beginning of a return to American isolationism. The final indication would be the victory of Warren Harding in the 1920 presidential election. Running on the platform of a ‘return to normalcy’, Harding would win the 1920 election in the most lopsided electoral victory in modern American history. American foreign policy would be quite unremarkable throughout the remainder of the 1920s, its primary concentration being “recovering its loans to Europe, [while] otherwise limiting its operations outside the hemisphere to ineffectual attempts to get Germany back onto its feet and restrain Japan from overdoing expansion into China” (Anderson, 2017, p. 16). Such an attitude accurately characterises the presidencies of the ‘roaring twenties’, who were dedicated to the pursuit of policies favourable to big business” (Dailey, 2018, p. 110), and undoing many of the progressive domestic reforms enacted over the previous 20 years (Dailey, 2018). Though the American economy would experience skyrocketing growth during this period, the speculative frenzy of the stock market and de-regulation of the American banking and finance sectors would soon lead to the complete breakdown of both the domestic and international financial system, driving home the fact that isolation in a modern interconnected economy was a fantasy (Dailey, 2018).

The Depression and Pre-War Years:

The importance of the Great Depression (1929-1939) on American foreign policy is that it drove home the realisation of the international character of modern economics, and the inability to stay economically isolated in a complex interwoven global economy (Anderson, 2017). One of the primary catalysts of the Great Depression was the complex debt triangle between the United States, Germany, and the Allied governments of France and Britain. Summed up easily by Jane Dailey: “Germany borrowed money from private American banks to help pay reparations to France and Britain, which in turn used those funds to repay their debts to the United States” (Dailey, 2018). Exacerbating this situation was the unwillingness of the American government to ease or forgive the $10 billion of debt owed to them by the Allied governments for loans made to them during the war (Dailey, 2018).

A crisis arose when the stock market nosedived in late 1929. In what became known as Black Monday and Black Tuesday, stocks plummeted 23% in two days, with billions of dollars lost (Salsman, 2004). Next, the banks failed as a result of the bank run of 1930, beginning in Louisville, Kentucky; “banks scrambled to meet this demand by calling in loans and selling assets, thereby driving down the value of assets in otherwise sound institutions and imperiling the entire banking system in an expanding ripple effect” (Dailey, 2018, p. 144). The banks needed cash to pay their depositors who began lining up all over the country, yet “the desperate effort of thousands of individual banks to meet the demands of their depositors contracted the money supply, tightened credit, and strangled the system as a whole” (Dailey, 2018, p. 155). The resulting liquidity crisis of 1930 led to the beginning of a European crisis; now that American banks were failing and didn’t have money to loan the Europeans, German and Austrian banks failed. Then, Great Britain defaulted on gold payments to investors. This European crisis caused investors to panic and begin an even larger run on American banks later in 1931, leading to an even larger liquidity crisis and the eventual failure of 2,294 American banks by the end of the year.

Archive Photos. (1929). New York Breadline. [Photograph]. NPR.Org.

The importance of the Great Depression to a history of foreign policy is primarily to illustrate how these developments shaped foreign policy during the time and also the relationship between foreign policy action and economics. In terms of the effect the Great Depression had on American foreign policy during the 1930s, it caused even deeper isolationism, spurred on by the need to focus energy and resources on the dire domestic situation (Rubin, 1966). In the turbulent events of the mid-1930s, including Japan’s occupation of Manchuria, the Spanish Civil War, and German remilitarisation, Congress would pass various Neutrality acts aimed at keeping the United States neutral and out of any conflict. Furthermore, after the German invasion of Poland, Americans who were polled overwhelmingly hoped for the defeat of Germany, but more than 90% opposed getting involved in the war — Holocaust.

The relationship between economics and foreign policy, which resulted from the Great Depression, is much more complex. As previously mentioned, the Great Depression brought home the idea that America was not safe across its two oceans from the fluctuations of the modern international financial system. Moreover, near the end of Roosevelt’s second term, rearmament in preparation for the world war began, leading to a resurgence of the American economy which would accelerate at a dizzying pace well beyond the end of the war. The lesson to be learned here is that “the internal fortunes of the American economy and external postures of the American state [would be] henceforth joined as they had never been before“ (Anderson, 2017, p. 17). In other words, beginning with the Great Depression, the consensus in American foreign policy was to seek in earnest to concern the United States deeply with shaping the international economic order for its own domestic economic profitability. Such a foreign policy spurned years earlier under Wilson, would lead to establishing a post-war world order based on the principles of free trade, and its political complement, liberal democracy (Anderson, 2017). In the logic of American foreign policy of the time and still to this day, “Such an economic order would be not only a guarantee of peaceful relations between states but allow the US to assume its natural place as first among them” (Anderson, 2017, p. 23). Yet this ideology would crystallise during and shortly after the war. In the pre-war years, despite the almost inevitability of another World War, and the stepped-up military preparedness of the United States, public opinion would remain deeply against another repeat of World War I.

U.S. Navy. (1945). US warships entering Lingayen Gulf. [Photograph].

America at War

With the outbreak of World War II (1939-1945) in Europe, America remained neutral, just as they had before during World War I. The American public and government, also just as during World War I, heavily favoured the Allied forces (Aleprete, 2007). Despite this, the war was still viewed as ‘not our problem’ (Dailey, 2018, p. 176), and an isolationist congress would make any political action nearly impossible (Dailey, 2018). Even after the destruction of Poland, Americans would not view the proceedings in Europe as a direct threat. One of the primary explanations for this, in the words of Jane Dailey, was that “just as the French had hoped the Belgians would bear the brunt of any war with Germany, and England had hoped to shield itself behind France, so the United States expected Britain to repel the Nazis while Americans remained secure on their side of the Atlantic” (Dailey, 2018, p. 178). With the breathtakingly successful invasion of France, and the beginning of heavy Luftwaffe bombing of civilian targets in Britain, the prospect of Axis domination in Europe, Asia, Africa, and the oceans became a serious possibility. In order to keep Britain from falling, American policymakers first began sending Britain arms under the “cash and carry” provision in 1939, and later, as the British economy became stretched, war materials were sent without payment under a “lend-lease principle” (Dailey, 2018, p. 179). With the entrance of Russia into the war in 1941, the lend-lease principle would be extended to all allied forces, establishing the United States as the ‘arsenal of democracy’, as it exported massive sums of oil, food, and war materials to the forces fighting the Nazis.

America would join the war officially after the Japanese bombing of Pearl Harbor on 7th December 1941, leading to a brutal Pacific campaign which would end with the dropping of two atomic bombs on Hiroshima and Nagasaki in 1945. At this point, the American economy, which was almost entirely geared towards the war economy, would undergo a production miracle. Six million women would enter the workforce, and the largest internal migration in American history would take place, as millions of Americans moved to the Sunbelt where America’s war industries were clustered (Dailey, 2018). This production miracle and the gearing of American mass production towards the singular goal of winning the war would lead commentators to comment that World War II was a war of production (Warm, 2002).

US Army. (1943). Tehran Conference. [Photograph]. Wikimedia Commons.

Deciphering American foreign policy during this time is a very difficult and complex process. In regards to the Soviet Union, Franklin Roosevelt (1882-1945) and especially Winston (1874-1965) Churchill were wary of their new ally and feared Bolshevism. While the Soviets shouldered the burden of fighting the Nazis throughout the War, Churchill postponed the opening of a second front for as long as possible in the hopes that the Soviet Union and the Nazis would bleed each other dry (Higgins, 1959). Partially as a result, the Soviets would lose an astonishing 24 million people by the end of the war. Yet, the Soviets “made clear the price the Allies would pay for having left the Red Army to fight the Nazis alone for nearly three years: neither Britain nor America would interfere with Soviet control over eastern Europe and the Baltic states” (Dailey, 2018, p. 188). As a result, when the tides of the war changed, so too did the horizons of American foreign policy in Europe. While the battles raged and Nazism continued, support of the USSR would be an absolute necessity in crushing Germany. Though as the war drew to a close, the architects of American foreign policy were already determining how to build up a post-war Germany which could act as a bulwark against Bolshevism and the further westward spread of the Soviet Union (Anderson, 2017).

The Post-War Order

As the war drew to a close, the contours of American foreign policy in the post-war years became clear: a complete reversal was in order. In Europe, Britain and the United States would have to build their former enemy Germany back up as a bulwark to hold back the Soviets (Anderson, 2017), while of a slightly lesser order was the task of containing the various left-wing resistance movements which had sprung up in France, Belgium, Italy, Yugoslavia, and Greece (Anderson, 2017). In Asia, on the other hand, Japan would have to be built up to counter China, which retained an incredible potential to become a world superpower in due time once it had been built up. Also, if China fell into the hands of the Communists, would constitute the principal threat to American and Western interests both in the Pacific and globally (Anderson, 2017). To build back Germany and Japan, a liberal democratic constitution would be the first piece, with a robust economic rehabilitation to take place alongside, along with preferential trading agreements and generous bilateral aid which would last until 1973 and the ending of the Bretton Woods system. In the end, the most important foreign policy of the United States during the war and post-war years can be summarised by this dichotomy: the support for the Soviet Union against Germany and Japan on the battlefield, but always with an eye to the end of the war and post-war global system governed by the United States.

Ragan, L. (1943). UN Fight for Freedom. [Poster]. Wikimedia Commons.

Invaluable to the establishment of this post-war order would be the creation of the United Nations. Its general idea was originally issued in the Atlantic Charter (1941), a proclamation of Anglo-American goals for the world in the post-war era. It would be expanded upon in late 1944 at Dumbarton Oaks as the war began to wind down, and would later be signed as the Declaration of the United Nations by most of the Allied nations including the Soviet Union which pledged to uphold its principles. These principles were primarily “the right of all peoples to choose the form of government under which they will live… improved labor standards, economic advancement, social security… [and] a wider and permanent system of general security“ (Dailey, 2018, p. 179). Just as with the League of Nations, despite the grand visions of global peace, Americans and other delegates worried about how such an organisation would limit sovereignty and the ability of nations to act completely freely. As such, an ‘escape clause’ article would be added to the charter, stating that “nothing contained in the present Charter shall authorize the United Nations to intervene in matters which are essentially within the domestic jurisdiction of any state or shall require the Members to submit such matters to settlement” (Dailey, 2018, p. 197).

Despite the idealistic pledges of Roosevelt and the United Nations, the creation of the U.N. and the post-war system that Franklin Roosevelt and planners in Washington D.C. had in mind also involved a cold calculus of power, as noted by the emerging 'realist' school of thought in international relations theory. To cite the words of Perry Anderson once again, the post-war order envisioned in Washington “would be not only a guarantee of peaceful relations between states but allow the US to assume its natural place as first among them” (Anderson, 2017, p. 23). By the end of 1945, such a stance was not only a reflection of the reality of power relations but almost a necessity, given the near complete destruction of the European and East Asian economies and social fabrics (Centre for Economic Policy Research, 2019). The United States, on the other hand, would retain an economy three times the size of the USSR, while being responsible for half the world’s industrial output and 75% of its gold reserves (Anderson, 2017). The institutional foundations which would reflect America’s dominance and a seat at the top of the new political world order would be the United Nations, while in the economic sphere the Bretton Woods accords would install the dollar as the “master of the international monetary system, the reserve currency against which all others had to be pegged” (Anderson, 2017, p. 26).


The years from 1919 to 1945 would mark a seismic shift in the history of American foreign policy. Whereas in the post-World War I years the United States had chosen to follow its historical isolationist current and withdraw in large part from international affairs, by the end of World War II in 1945 America would find itself at the top of a new global order, embracing its Wilsonian duty. The events of the Great Depression and the global destruction of the Second World war had brought home the lesson in Washington that American isolationism was not only any longer desirable, but no longer possible in the modern age. For better or worse, World War II had driven home the idea that America could no longer hide behind its two oceans, and had a responsibility to step out into the international scene and dictate events, frequently for their own self-interest.

Bibliographical References

Aleprete, M. E. (2007). The Path to American Intervention in the First World War: Implications for Understanding the Foreign Policy Choices of Democratic States. Democracy and Security, 3(2), 189–214. https://www.jstor.org/stable/48602584

Anderson, P. (2017). American Foreign Policy and Its Thinkers (Reprint ed.). Verso.

Braeman, J. (1983). The New Left and American Foreign Policy during the Age of Normalcy: A Re-Examination. The Business History Review, 57(1), 73–104. https://doi.org/10.2307/3114395

Brown, C. (2019). Understanding International Relations (5th ed.). Springer.

Centre for Economic Policy Research. (2019, November 21). Recovery and reconstruction: Europe after WWII. CEPR. https://cepr.org/voxeu/columns/recovery-and-reconstruction-europe-after-wwii

"Covenant of the League of Nations". The Avalon Project. Archived from the original on 26 July 2011. Retrieved 30 August 2011.https://web.archive.org/web/20110726080156/http://avalon.law.yale.edu/20th_century/leagcov.asp

Dailey, 2018, J. (2018). Building the American Republic, Volume 2: A Narrative History from 1877 (1st ed.). University of Chicago Press.

Higgins, T. (1959). Winston Churchill and the Second Front. International Affairs (Royal Institute of International Affairs 1944-), 35(2), 278–280. http://www.jstor.org/stable/2605444

Magliveras, K. D. (1999). Exclusion from Participation in International Organisations: The Law and Practice behind Member States' Expulsion and Suspension of Membership. Martinus Nijhoff Publishers. ISBN 978-90-411-1239-2.

Nag, O. S. (2017, April 25). Largest Landslide Victories In US Presidential Election History. WorldAtlas. https://www.worldatlas.com/articles/largest-landslide-victories-in-us-presidential-election-history.html

Rubin, R. I. (1966). The Persistence of American Isolationism. Pakistan Horizon, 19(3), 241–248. http://www.jstor.org/stable/41393813

Salsman, R. M. "The Cause and Consequences of the Great Depression, Part 1: What Made the Roaring '20s Roar", The Intellectual Activist, ISSN 0730-2355, June 2004, p. 16.

United States Holocaust Musuem. (2022). The United States: Isolation-Intervention. Holocaust Encyclopedia. https://encyclopedia.ushmm.org/content/en/article/the-united-states-isolation-intervention

Warm, T. (2002). Wartime Production. OAH Magazine of History, 16(3), 47–52. http://www.jstor.org/stable/25163526

Visual Sources

Archive Photos. (1929). New York Breadlin [Photograph]. NPR.Org. https://www.npr.org/sections/money/2017/03/15/520294083/episode-522-the-invention-of-the-economy

(n.d.). (1929). A solemn crowd gathers outside the Stock Exchange after the crash [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Crowd_outside_nyse.jpg

Dart, H. G. (1919). Uncle Sam Should’ve Stayed Home [Cartoon]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:UncleSamShouldveStayedHome.jpg

Ragan, L. (1943). UN Fight for Freedom [Poster]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:UN_Fight_for_Freedom_Leslie_Ragan_1943_poster.jpg

US Army. (1943). Tehran Conference [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Tehran_Conference,_1943.jpg

U.S. Navy. (1945). US warships entering Lingayen Gulf [Photograph]. https://commons.wikimedia.org/wiki/File:US_warships_entering_Lingayen_Gulf_1945.jpg

Author Photo

Taylor Pace

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