From non-intervention to collective defence

Franklin D Roosevelt took office in 1933, as Japanese expansion in Asia and the rise of aggressive regimes in Europe threatened the international order. Most American republics initially tried to preserve peace through neutrality, non-intervention and closer inter-American consultation.

At the Montevideo Conference of 1933, the United States accepted the principle that states should not interfere in one another’s internal or external affairs. The Buenos Aires Conference of 1936 established consultation if peace in the hemisphere came under threat. In 1938, the Lima Conference reaffirmed continental solidarity as war drew closer in Europe.

War began in September 1939. The Panama Conference then declared American neutrality and proposed a maritime security zone around much of the hemisphere. The United States remained formally neutral, but its policy steadily shifted towards supporting the Allies. The 1939 “cash-and-carry” provision allowed belligerents to purchase arms, the destroyers-for-bases agreement of 1940 strengthened Atlantic defence, and the Lend-Lease Act of March 1941 supplied states resisting the Axis.

The fall of France and the Netherlands created fears that their American colonies could come under Axis influence. At Havana in 1940, the American republics agreed that European possessions in the hemisphere could be placed under collective administration if necessary. Neutrality, therefore, did not mean indifference to hemispheric security.

Pearl Harbor on 7 December 1941 changed the situation completely. Most American states either broke relations with the Axis or declared war on it, although their military participation varied. At the Rio Conference in January 1942, the republics recommended breaking diplomatic relations with the Axis. Brazil became a close US military partner. Argentina, however, maintained formal neutrality until March 1945, though it broke diplomatic relations with the Axis in January 1944, creating tension with Washington.

Roosevelt’s Good Neighbor policy

The Good Neighbor policy largely replaced direct US military intervention with consultation, non-intervention, trade and diplomatic cooperation. US power in Latin America did not disappear, but the way Washington used that power changed.

Important applications included:

• US acceptance of non-intervention at Montevideo in 1933.
• The abrogation of the Platt Amendment in 1934, which reduced the formal US right to intervene in Cuba.
• The withdrawal of US forces from Haiti in 1934.
• Restraint after Mexico nationalized foreign oil holdings in 1938; the dispute was eventually settled through negotiation rather than armed intervention.
• Reciprocal trade agreements, cultural diplomacy and wartime military assistance intended to bind the hemisphere more closely to the United States.

The policy improved Washington’s relations with many Latin American governments and made wartime cooperation easier. Airfields, naval facilities, raw materials and intelligence networks helped protect the Panama Canal, Caribbean shipping and routes across the South Atlantic. Nelson Rockefeller’s Office of the Coordinator of Inter-American Affairs also promoted hemispheric solidarity through radio, film and cultural programmes.

Its limits mattered just as much. Cooperation remained unequal because the United States had far greater economic and military power. Washington also tolerated authoritarian governments when they supported hemispheric security. The Good Neighbor policy therefore brought a genuine change in method—from occupation towards negotiation—but US influence did not disappear.

Competing interpretations

Diplomatic historians often emphasize the practical success of consultation. The United States gained wartime partners without repeating the occupations associated with earlier interventionism. More critical interpretations stress continuity, arguing that economic pressure and strategic dependence allowed Washington to preserve informal control. The policy can be understood both as a genuine improvement in inter-American relations and as a more acceptable form of US leadership.

The guide allows the class to choose any two countries from the Americas. This section uses the United States and Canada as worked examples. Both made major contributions, although Canada entered the war in 1939 and the United States did not formally enter until December 1941.

United States

Before formally entering the war, Roosevelt’s administration supported Britain and the other Allied powers while preparing the United States for conflict. Through the Selective Training and Service Act of 1940, Congress approved the first peacetime draft in US history. The destroyers-for-bases agreement, Lend-Lease and undeclared naval assistance in the Atlantic made the line between neutrality and participation increasingly difficult to maintain.

Japan’s attack on Pearl Harbor led to a US declaration of war on 8 December 1941. Germany and Italy declared war on the United States on 11 December. The United States fought across two oceans and became the Allied coalition’s principal industrial supplier.

In Europe and North Africa, US forces took part in Operation Torch in November 1942, followed by the invasions of Sicily and Italy in 1943 and the Normandy landings on 6 June 1944. American forces moved through France and into Germany. Britain, the Soviet Union and the United States worked together on strategic planning, though they continued to disagree about the timing of a cross-Channel invasion and the shape of the post-war settlement.

In the Pacific, the United States recovered from Pearl Harbor through carrier warfare and industrial expansion. The Battle of Midway in June 1942 stopped Japanese offensive momentum. Later campaigns used “island hopping”: US forces seized strategically important positions while bypassing others. Fighting at Guadalcanal, the Philippines, Iwo Jima and Okinawa brought them closer to Japan, but also showed the likely cost of continued resistance.

US participation proved decisive because it combined industrial capacity, large armed forces and global logistics. Victory still depended on coalition warfare. Britain and the Commonwealth had sustained the conflict before US entry, while the Soviet Union carried much of the land war against Germany.

Canada

Canada declared war on Germany on 10 September 1939, one week after Britain. By making a separate declaration, Canada demonstrated the greater constitutional autonomy it had gained since the First World War.

Canada’s longest-running contribution was the Battle of the Atlantic. The Royal Canadian Navy expanded rapidly and escorted merchant convoys carrying troops, food and matériel to Britain. Canadian ports, especially Halifax, became vital parts of the Atlantic supply system. Canada also hosted much of the British Commonwealth Air Training Plan, training aircrew from across the Commonwealth.

Canadian forces were defeated at Hong Kong in December 1941 and suffered heavy losses during the Dieppe Raid in August 1942. The raid shaped later amphibious planning, although historians disagree about how far the knowledge gained justified its costs.

Canadian troops fought in Sicily and Italy from 1943. On D-Day, the 3rd Canadian Infantry Division landed at Juno Beach. Canadian forces later helped clear the Scheldt estuary in 1944, opening Antwerp to Allied shipping. They also took part in the liberation of the Netherlands in 1944–45.

Canada became an important middle power, rather than simply a British auxiliary. Its contribution was substantial for a country of its population. At the same time, dependence on US industry and continental defence arrangements pulled Canada more firmly into the United States’ strategic orbit.

Comparison

Wartime society

The war gave governments across the Americas much greater authority. They directed labour, controlled prices and supplies, raised taxes, rationed consumer goods and used propaganda to promote production and national unity. Wartime industry also sped up migration towards cities and industrial centres, putting housing and public services under strain.

In the United States, migration changed the West Coast and the industrial cities of the North. Canada saw a similar movement into urban employment as munitions production expanded and the military recruited more personnel. These shifts disrupted established communities and opened new opportunities. They also increased competition for jobs, housing and public space.

Women

As men left for military service, war production created new jobs for women. In the United States, wartime propaganda showed women working in aircraft plants, shipyards and other industries previously associated with male labour. Women also served in organizations such as the Women’s Army Corps and the Navy’s WAVES, usually in non-combat roles.

Canadian women took jobs in munitions, agriculture and administration. They also served through bodies including the Canadian Women’s Army Corps and the women’s divisions of the air force and navy. Governments and employers described this work as patriotic service, while often keeping women on lower pay and placing them in gendered job categories.

The war gave women more experience of paid employment and showed that they could work in skilled occupations. The changes had clear limits, though. Women still carried out most domestic work, and official policy generally assumed that returning servicemen would take back many of their jobs. The war challenged gender expectations without removing them.

Minorities

African Americans moved to defence-production centres during another phase of the Great Migration. Activists connected victory over fascism abroad with victory over racism at home. Pressure from A Philip Randolph, together with a proposed march on Washington, helped lead to Roosevelt’s Executive Order 8802 in 1941. The order prohibited discrimination in defence employment and created the Fair Employment Practice Committee.

These gains existed alongside segregated armed forces, discrimination in housing and racial violence. The Detroit riot of 1943 showed that mobilization could intensify racial conflict as well as create economic opportunities.

Mexican Americans entered military service and defence work in large numbers. Established by the United States and Mexico in 1942, the Bracero programme brought Mexican labourers into US agriculture and railway work. Demand for labour created opportunities, but discrimination remained. The Zoot Suit violence in Los Angeles in 1943 exposed hostility towards Mexican American youth.

Indigenous people served in the armed forces and worked in wartime industries. In the Pacific, Navajo code talkers used their language for secure military communications. Military service could strengthen claims to citizenship and equality, but it did not end poverty, discrimination or pressure on Indigenous cultures and lands.

Japanese Americans, Japanese Latin Americans and Japanese Canadians faced state-directed exclusion and confinement. Their treatment is examined separately in HL2.13.4.

Conscription

The United States introduced conscription through the Selective Training and Service Act of September 1940. After Pearl Harbor, conscription provided the personnel needed for a global war. Although the policy was broadly accepted after the attack, its administration reflected existing inequalities, including segregation within the armed forces.

Canada introduced the National Resources Mobilization Act in 1940. It allowed compulsory service for home defence but initially protected Prime Minister William Lyon Mackenzie King’s pledge against overseas conscription. A 1942 plebiscite released the government from this promise. Quebec largely opposed releasing it, while every other province largely supported doing so. Heavy casualties in Europe led to the conscription crisis of 1944, when the government sent a limited number of conscripts overseas.

The Canadian crisis showed continuity with the linguistic and political divisions exposed during the First World War. King’s gradual approach avoided a complete national rupture, but it satisfied neither committed conscriptionists nor French Canadian opponents.

Overall impact

The war accelerated urbanization, broadened employment and raised expectations of social equality. It also strengthened federal governments and revealed deep racial, ethnic and linguistic divisions. Social change was uneven. Wartime necessity opened doors for some groups, while state policy and popular prejudice closed them for others.

Japanese Americans

After Pearl Harbor, military officials and politicians depicted people of Japanese ancestry on the West Coast as a security threat. Wartime fear and racial prejudice drove these claims. No evidence showed that the community as a whole was involved in espionage or sabotage.

On 19 February 1942, Roosevelt issued Executive Order 9066. The order authorized military exclusion zones without identifying a particular ethnic group, but officials applied it mainly to Japanese Americans. Issei immigrants and their US-born Nisei children were removed from the West Coast. Families were initially held in temporary assembly centres before being confined in camps run by the War Relocation Authority, including Manzanar in California and Heart Mountain in Wyoming.

Removal cost people their homes, farms, businesses and personal property. Camp residents lived under armed supervision in isolated locations. The government also used a loyalty questionnaire to classify inmates, which created divisions within the community. Japanese American soldiers, including the 442nd Regimental Combat Team, served in the US military even while their families remained confined.

Legal challenges revealed the tension between military authority and civil liberties. In Korematsu v United States in December 1944, the Supreme Court upheld Fred Korematsu’s conviction for violating an exclusion order. On the same day, Ex parte Endo ruled that the government could not detain a citizen whose loyalty it conceded. The exclusion orders ended afterwards.

Japanese Latin Americans

The United States worked with several Latin American governments to remove people of Japanese ancestry from Latin America. Peru supplied the largest group. Deportees were taken to the United States and held at sites including the internment camp at Crystal City, Texas.

Some were treated as potential exchange hostages who could be traded for civilians held by Axis powers. Many had committed no offence and were given no meaningful individual hearing. Since deportation and wartime policies often prevented them from returning to their countries of residence, some faced serious obstacles when they tried to go back.

This policy shows that wartime confinement extended beyond a domestic US measure. It formed part of a hemispheric security system shaped by US diplomatic pressure, racial suspicion and the use of civilians as instruments of war.

Japanese Canadians

After Pearl Harbor, the Canadian government removed people of Japanese ancestry from the protected coastal zone of British Columbia. Orders-in-Council supplied the legal machinery for exclusion, detention and property control. As in the United States, the policy affected citizens as well as immigrants and did not require proof of individual disloyalty.

Officials initially separated men for road-camp labour. Families were sent to settlements and camps in the interior of British Columbia, while others worked on sugar-beet farms farther east. The Custodian of Enemy Property took control of homes, fishing boats, farms and businesses. These assets were then sold without the owners’ consent, making removal economically destructive as well as socially traumatic.

By 1945, Japanese Canadians were pressured either to move permanently east of the Rocky Mountains or to go to Japan. Coastal exclusion had therefore developed into forced dispersal.

Comparison and interpretation

At the time, defenders presented these measures as military precautions taken after Pearl Harbor. The explanation is weakened by the lack of individualized evidence and by the use of ancestry as a substitute for demonstrated risk. Historians therefore place greater weight on racial prejudice, economic interests, political pressure and the broad emergency powers claimed by wartime governments.

The decision in 1945

The Manhattan Project produced the first atomic weapons through a secret programme led by the United States with British and Canadian cooperation. The successful Trinity test in New Mexico on 16 July 1945 confirmed that an atomic device could work.

President Harry S Truman, who took office after Roosevelt’s death in April 1945, approved use of the new weapon against Japan. An Interim Committee considered the issue and recommended military use without a prior demonstration. A target committee selected cities that combined military significance with urban areas large enough for the weapon’s effects to be observed.

On 26 July, the United States, Britain and China issued the Potsdam Declaration demanding Japan’s unconditional surrender and warning of “prompt and utter destruction.” Japan did not accept the demand. The United States dropped a uranium bomb on Hiroshima on 6 August and a plutonium bomb on Nagasaki on 9 August. The Soviet Union entered the war against Japan on 8 August and attacked Japanese forces in Manchuria on 9 August. Japan announced its acceptance of surrender on 15 August; the formal surrender followed on 2 September 1945.

Reasons for using the bombs

The central stated reason was to compel rapid Japanese surrender. Fighting at Iwo Jima and Okinawa had shown that Japanese forces could resist fiercely even when defeat appeared inevitable. US planners feared that an invasion of the Japanese home islands would cause heavy casualties among American troops, Japanese forces and civilians.

Other considerations reinforced the decision:

• US leaders wanted to end the war before further casualties accumulated through conventional bombing, blockade and continued fighting in Asia.
• Japanese leaders remained divided, and the military had not accepted unconditional surrender.
• The United States had invested extensive resources in the Manhattan Project and possessed a weapon believed capable of producing a decisive psychological shock.
• A rapid end to the war could limit Soviet participation in the occupation of Japan and strengthen the US position in post-war diplomacy.
• The atomic bombings occurred in the context of existing large-scale strategic bombing, including the firebombing of Tokyo.

The choice of Nagasaki remains especially controversial because only three days separated the attacks. Critics argue that there was insufficient time to judge Hiroshima’s political effect or the consequences of Soviet entry.

Significance

The immediate significance was Japan’s surrender and the end of the Second World War. Atomic bombing was not the only pressure on Japan: naval blockade, conventional bombing, military defeat and Soviet entry also influenced the decision. The relative importance of these factors remains disputed.

The bombings killed civilians on a massive scale through blast, heat, fire and radiation. Survivors experienced long-term illness and social stigma. Hiroshima and Nagasaki therefore became central to arguments about whether military necessity can justify weapons whose effects cannot be confined to combatants.

Strategically, the attacks began the nuclear age. The United States briefly held an atomic monopoly and emerged from the war with unmatched destructive power. At the same time, the bombings contributed to the emerging Cold War and later nuclear arms race, while the Soviet Union also developed nuclear weapons.

Historical interpretations

Traditional interpretations emphasize military necessity. They argue that the bombs ended the war quickly, avoided an invasion and saved lives that would otherwise have been lost in prolonged combat.

Revisionist interpretations place greater emphasis on diplomacy. They argue that Japan was already near defeat and that demonstrating US power to the Soviet Union influenced the decision. Modifying the demand for unconditional surrender or waiting for Soviet entry were proposed alternatives, but whether either would have secured surrender without attacking cities cannot be known.

A combined interpretation treats rapid surrender as a primary objective while also considering casualty fears, domestic politics, bureaucratic momentum, assumptions about strategic bombing and concern about Soviet influence. The dispute persists because the alternatives—demonstration, blockade, modified surrender terms or invasion—have outcomes that cannot be known with certainty.

The guide allows the class to select any two countries from the Americas. This section uses the United States and Canada as worked examples, so their experiences can be compared directly: one was a new global superpower, while the other was a closely connected middle power.

United States: economic effects

Wartime mobilization completed the recovery from the Great Depression. Federal spending created demand for labour and industrial output, and conscription reduced civilian unemployment. Factories that had made automobiles and consumer goods were converted to produce aircraft, tanks, ships and other military equipment.

The War Production Board set industrial priorities. Taxation, war bonds, rationing and price controls then directed resources towards the military. Large corporations received major government contracts, while small firms, farmers and workers also benefited from high demand. As people moved towards industrial centres, the South and West grew more quickly.

The war greatly increased federal control over the economy. Organized labour also became stronger, although strikes and wage disputes continued. Women and minority workers entered industries that had previously excluded them. Their gains, however, remained vulnerable to discrimination and to changes in employment after the war.

By 1945, the United States had enormous industrial capacity, strong financial reserves and a commanding position in world trade. Unlike the principal European and Asian powers, it had not suffered devastation to its mainland infrastructure. This economic strength became the foundation for its post-war diplomatic influence.

United States: diplomatic effects

The war ended the possibility of returning to traditional isolation. Roosevelt took part personally in Allied summit diplomacy and worked with Winston Churchill and Joseph Stalin on military strategy and the post-war order. By 1945, disagreements over Eastern Europe and Soviet influence were already clear.

The United States took the leading role in designing new international institutions. The Bretton Woods Conference of 1944 established the basis for the International Monetary Fund and the World Bank, with the dollar at the centre of the new monetary system. The United Nations Charter was signed at San Francisco in June 1945, and the United States became a permanent member of the Security Council.

The country emerged as a global superpower, with military commitments in Europe, Asia and the Pacific. Its atomic monopoly strengthened this position. At the same time, rivalry with the Soviet Union began to replace the wartime alliance.

Canada: economic effects

Canada’s industrial expansion accelerated as its factories supplied Britain and the wider Allied war effort. Shipbuilding, aircraft production, vehicles, metals and munitions became major sectors. Agriculture remained essential too, since Canada supplied food to Britain and Allied forces.

The federal government created Crown corporations, controlled prices and wages, rationed goods and raised revenue through taxation and Victory Bonds. Full employment and high demand increased incomes, but shortages and state controls restricted civilian consumption. Regional economies became more closely connected within a national war economy.

Mobilization strengthened the federal government in relation to the provinces. It also sped up urbanization and brought more women into paid industrial work. Canada ended the war with a larger, more diverse industrial base, though converting military production to civilian production posed a major challenge.

Canada: diplomatic effects

Canada’s independent declaration of war and substantial military contribution reinforced its separate international identity. It increasingly operated as a middle power: it could not determine the international system, but it could make a significant contribution to coalitions and institutions.

Canada also became more closely integrated with the United States. The Ogdensburg Agreement of 1940 created the Permanent Joint Board on Defence, while the Hyde Park Declaration of 1941 coordinated wartime production. These arrangements shifted Canada’s strategic and economic centre of gravity away from Britain and towards North America.

Canada took part in creating the United Nations and signed its Charter in 1945. Its wartime experience encouraged support for collective security and multilateral diplomacy. Through these approaches, a middle power could exert more influence than its military strength alone would have allowed.

Comparison

Economic and diplomatic change were inseparable. US productive power made global leadership possible. Canada’s wartime production and military effort, meanwhile, gave it greater diplomatic standing. The same process also increased Canada’s dependence on the much larger US economy and defence system.