The End of Isolationism

This section explores how America evolved from an isolationist foreign policy to an active one. After the First World War, the United States’ foreign policy shifted towards isolationism, with many Americans wanting to avoid entanglement in international conflicts and politics. The nation’s reluctance to become involved in foreign affairs was evident when it did not join the League of Nations, an international peacekeeping body created in 1920. However, by the end of 1941, America had abandoned its policy of isolationism and entered World War Two following the attack on Pearl Harbor.

Isolationism and the Neutrality Acts

In the years following the First World War, a growing belief took hold that America had been dragged into the conflict due to the influence of munitions manufacturers, industrialists, and financiers. In 1934, Congress appointed a committee, known as the Nye Committee, to investigate the reasons behind the United States' involvement in the war. The committee’s key conclusion was that American arms dealers and financiers had played a significant role in encouraging the country’s entry into the war, seeking to make large profits by supplying weapons to the Allies.

Although the committee did not provide any specific evidence of conspiracy, the idea that lobbyists had manipulated the government became a popular belief. To prevent this from happening again, Congress passed a series of Neutrality Acts between 1935 and 1937, designed to keep the US out of foreign conflicts. These laws made it illegal for the US to sell weapons, provide loans, or extend credit to nations involved in war, regardless of whether they were the aggressors or the victims.

However, as the outbreak of World War Two loomed, President Franklin D. Roosevelt recognised that these limitations might be detrimental to American interests, especially as tensions in Europe began to escalate. In 1939, after the war in Europe had already begun, Roosevelt introduced the Cash and Carry policy. This policy allowed belligerent nations to purchase war materials from the US, provided they paid cash and used their own ships to transport the goods. While it kept America technically neutral, it enabled Britain and France to obtain critical war supplies to fight against Nazi Germany.

Lend-Lease Act

As the war in Europe dragged on and Britain’s financial resources dwindled, Roosevelt began to feel that isolationism was no longer in the best interests of the US. In late 1940, during one of his famous fireside chats, Roosevelt introduced the idea of the US becoming the "arsenal of democracy." He proposed that America should lend or lease military supplies to countries whose defence was vital to the security of the United States, bypassing the restrictions of the Neutrality Acts.

In March 1941, the Lend-Lease Act was passed, officially allowing the US to provide military aid to nations fighting the Axis powers, particularly Britain, which was struggling to resist Nazi Germany. Under the terms of the act, the US sent weapons, aircraft, warships, and other essential supplies to Britain, the Soviet Union, China, and other nations. By the end of 1941, Britain had received over $7 billion worth of military equipment and supplies from the US, significantly boosting its war effort.

The Attack on Pearl Harbor

In the 1930s, tensions between the United States and Japan had been rising. Japan’s growing militarism and territorial expansion, particularly in China, were of great concern to America. In 1937, Japan invaded China, and in 1940, it formed a military alliance with Germany and Italy, known as the Axis Powers.

In response, the United States increased its aid to China and imposed economic sanctions on Japan, including a ban on oil and steel exports. Japan, reliant on American oil for its war machine, was pushed into a corner. While there were diplomatic negotiations to resolve the crisis, the Japanese government decided to take a more aggressive approach. They viewed war with the United States as inevitable if they were to maintain control over the Pacific region.

On 7 December 1941, Japan launched a surprise attack on Pearl Harbor, a major US naval base in Hawaii. The attack was devastating—most of the US Pacific Fleet, including eight battleships, were either destroyed or severely damaged, and over 180 aircraft were lost. Approximately 2,400 Americans were killed, with many more injured.

This attack marked a turning point for the United States. The following day, 8 December 1941, Congress almost unanimously passed a declaration of war against Japan, formally bringing the United States into World War Two. In retaliation, Germany and Italy declared war on the United States on 11 December 1941, thereby solidifying America’s entry into the global conflict.

The Shift in US Foreign Policy

The events leading up to and following the attack on Pearl Harbor illustrate the dramatic shift in US foreign policy. For over two decades after the First World War, the United States had sought to avoid foreign entanglements. Yet, the aggression of Nazi Germany, Fascist Italy, and Imperial Japan made it clear that the world order was under threat, and the US could no longer remain neutral.

While many Americans had initially embraced isolationism in the interwar years, fearing the costs and consequences of involvement in another global conflict, the attack on Pearl Harbor united the country in a shared resolve to fight the Axis powers. Roosevelt had to navigate the pressures of isolationism, particularly from conservative and anti-war factions, but ultimately, the events of 1941 cemented America’s role as a central player in World War Two.

This shift also marked the end of America’s longstanding policy of isolationism and the beginning of its active engagement in international affairs, leading to a new global order after the war. The US became a key founding member of the United Nations in 1945, and its involvement in world politics would continue to grow in the decades that followed.