In 1914 the USA wanted no part of Europe's war. President Woodrow Wilson declared neutralityneutrality, and most Americans agreed — this was, in their eyes, someone else's fight.
That changed by 1917. German unrestricted submarine warfare was sinking American ships, and the intercepted Zimmermann Telegram revealed Germany had offered Mexico an alliance against the USA. Congress declared war in April 1917.
- Fresh troops and money — by 1918 over a million US soldiers (the AEF) had reached France, tipping an exhausted stalemate toward an Allied breakthrough.
- Economic muscle — US loans and supplies had already been propping up Britain and France since 1915; entry made that support official and unlimited.
- A new kind of peace demand — Wilson didn't just want victory, he wanted to redesign how nations dealt with each other afterward.
Wilson's Fourteen Points: In January 1918 Wilson set out Fourteen Points for a fair peace: self-determination for nations, open diplomacy instead of secret treaties, freedom of the seas, reduced armaments — and, as point 14, a League of NationsLeague of Nations to keep the peace permanently.
At the Paris Peace Conference in 1919, Wilson fought hard to get the League written into the Treaty of Versailles. He succeeded — but back home, the US Senate had the final word, and it said no.
Why the Senate rejected the League
- Article 10 committed members to defend each other if attacked — Republicans like Henry Cabot Lodge feared this dragged the USA into every future European war automatically.
- Many Americans wanted to return to isolationismisolationism after the costs of 1917–18.
- Wilson refused Lodge's compromise reservations, then suffered a stroke in October 1919 — he could no longer campaign or negotiate.
Why Wilson believed the League mattered
- Collective security could stop small conflicts becoming world wars, exactly as 1914 had shown they could.
- US moral leadership and economic power made it the natural anchor of any new peace system.
- Without the USA, the League would lack its most powerful potential member — weakening it from birth.
The irony: The League of Nations was Wilson's idea — yet the USA, its own architect, never joined. This is one of the most argued-over ironies in Paper 3: did Wilson's stubbornness or the Senate's isolationism do more damage to the peace?
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Before the 1930s, the USA had a habit of sending Marines into Latin America and the Caribbean whenever it judged its interests at risk — Nicaragua, Haiti, and the Dominican Republic all saw US troops occupy them for years.
President Franklin D. Roosevelt changed the tone in 1933 with the Good Neighbor PolicyGood Neighbor Policy. In his inaugural address he pledged the USA would be "the neighbor who resolutely respects himself and, because he does so, respects the rights of others."
Renouncing intervention
The 1933 Montevideo Conference had the USA formally accept non-intervention in the internal affairs of other American states.
Withdrawing troops
US Marines left Haiti in 1934 and Nicaragua earlier; military occupations that had lasted decades finally ended.
Cutting the Platt Amendment
In 1934 the USA gave up its treaty right to intervene in Cuba, though it kept its naval base at Guantánamo Bay.
Building Pan-American ties
The USA promoted trade deals and cooperation through the Pan-American Union, aiming for influence through goodwill rather than force.
Respect, withdraw, renounce, cooperate — Good Neighbor swapped the Marines for handshakes.
Tested by Mexico, 1938: When Mexico's President Cárdenas nationalized foreign-owned oil companies in 1938 — including US firms — Washington did not send troops as it once might have. Instead it negotiated compensation. This is often cited as proof the Good Neighbor Policy was a real shift, not just words.
But the policy had limits. The USA still backed friendly dictators who kept order and protected US business interests — for example the Somoza family in Nicaragua and Trujillo in the Dominican Republic stayed in Washington's good graces for decades.
Genuine change
- Formal treaty commitments to non-intervention (Montevideo 1933, Buenos Aires 1936) were new and real.
- Troops actually left occupied countries — a concrete, visible change from the 1900s–20s.
- Latin American governments got a genuine say in Pan-American forums for the first time.
Continuity of control
- US economic dominance over the region (companies, loans, trade terms) barely changed.
- Supporting friendly strongmen achieved the same stability the Marines used to provide — just more cheaply.
- The policy was partly a cost-saving and image-repair move during the Depression, not pure goodwill.
Frame it with significance: A strong Paper-3 answer weighs both sides: Good Neighbor changed the method of US regional power (diplomacy over Marines) while its underlying goal — a hemisphere safe for US interests — stayed constant.
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In the 1930s the USA again leaned isolationist. Congress passed Neutrality Acts (1935–37) banning arms sales and loans to countries at war, determined not to repeat 1917.
FDR still found ways to help Britain — through Lend-Lease in 1941, supplying weapons without demanding immediate payment. Then, on 7 December 1941, Japan attacked Pearl Harbor, destroying much of the US Pacific Fleet. The USA declared war the next day, and Germany and Italy declared war on the USA days later.
| US contribution | What it looked like |
|---|---|
| Industrial output | "Arsenal of democracy" — factories retooled for tanks, planes, and ships at a scale no other combatant could match |
| Two-front war | Fought simultaneously in the Pacific (against Japan) and in Europe/North Africa (against Germany and Italy) |
| D-Day and beyond | US troops led the 1944 Normandy landings alongside Britain and Canada, pushing into Germany by 1945 |
| The atomic bomb | The secret Manhattan ProjectManhattan Project produced the weapons dropped on Hiroshima and Nagasaki in August 1945 |
The atomic bomb debate: President Truman ordered the bombs dropped to force Japan's surrender without a costly invasion of its home islands. Historians and contemporaries have argued fiercely ever since: was it necessary to end the war and save lives, or was Japan already close to defeat, making the bombing more about warning the Soviet Union? Both arguments use real evidence — that's exactly the kind of debate Paper 3 rewards you for weighing.
Now compare Brazil — the other major Americas power in this micro. Brazil, under President Getúlio Vargas, spent the early war years playing both sides.
- Trading with both blocs — Vargas sold Brazilian coffee, cotton, and rubber to Germany and the Allies alike, extracting the best deals from each.
- Courted by Washington — the USA wanted Brazil's Atlantic coastline (a base for anti-submarine patrols) and its raw materials, so it offered loans and the Volta Redonda steel mill in exchange for cooperation.
- Pushed toward the Allies — German U-boats sinking Brazilian merchant ships in 1942 turned public opinion firmly against the Axis.
- Declared war in 1942 — Brazil joined the Allies, and its Brazilian Expeditionary Force fought in the Italian campaign from 1944, the only Latin American ground troops to fight in Europe.
Neutral is a choice, not an accident: Brazil's early neutrality wasn't passive waiting — Vargas actively used it as leverage to win concessions from both the Allies and the Axis before deciding. That bargaining is worth naming explicitly in an essay.