This unit follows the United States as it went from a continental power to a world power, starting with the overthrow of Hawaii's queen in 1893 and ending with the Senate's rejection of the Treaty of Versailles in 1919-1920. By the end, you should be able to explain why Americans expanded overseas, how World War I changed life at home, and why the U.S. turned down Wilson's plan for the peace.
Read the overview first, then work through each topic note and answer its checkpoint before you look at the common mistakes.
Unit 9 covers about 30 years when the U.S. stepped onto the world stage. It starts with the arguments for empire in the 1890s and moves through two wars and a peace conference. Throughout, Americans debated whether expansion matched or betrayed the country's founding ideals.
Honors US History Unit 9 covers American imperialism and World War I, roughly 1890 to 1920. You study why the U.S. expanded overseas, including economic needs, Alfred Thayer Mahan's naval theories, and Social Darwinism. You also study the annexation of Hawaii, the Spanish-American War of 1898, and the Philippine-American War that followed. In Latin America, the unit covers the Panama Canal and the Roosevelt Corollary. The second half covers U.S. neutrality and entry into World War I in 1917, the home front (the War Industries Board, the Espionage and Sedition Acts, the Great Migration), and Wilson's Fourteen Points. It ends with the Senate's rejection of the Treaty of Versailles and the League of Nations. Exact coverage varies by school.
Some business leaders argued that factories produced more than Americans could buy and looked to foreign markets, especially after the Panic of 1893. Mahan's 1890 book argued that a great nation needed a strong navy plus overseas coaling stations. That is why the U.S. targeted islands and canals like Hawaii, Guam, and Panama instead of huge territories.
The U.S. entered the war in 1898 claiming it wanted to free Cuba. It came out owning Puerto Rico, Guam, and the Philippines. The Anti-Imperialist League argued that ruling Filipinos without their consent broke the principles of the Declaration of Independence, and the brutal Philippine-American War of 1899-1902 gave them evidence.
Agencies like the War Industries Board managed the economy, and the Espionage and Sedition Acts punished dissent. Overseas, Wilson's Fourteen Points called for a League of Nations and greater self-government for some national groups. The Senate refused to commit the U.S. to that League, so the country ended the war powerful but unwilling to lead a collective security system.
Every event in this unit forced Americans to weigh national interest against the ideals of self-government and liberty. Imperialists said expansion spread civilization, and anti-imperialists said it made the U.S. a hypocrite. During World War I, the government limited free speech in the name of defending democracy. If you can trace that tension from Hawaii in 1893 to the Senate vote in 1920, you understand the unit.
In the 1890s, Americans advanced overseas expansion for economic, strategic, and ideological reasons.
Cubans rose against Spanish rule in 1895.
When war broke out in 1914, Wilson declared neutrality, but American money flowed toward the Allies.
In January 1918, Wilson laid out his Fourteen Points, which called for open diplomacy, freedom of the seas, free trade, arms reduction, greater self-government for some national groups, and a League of Nations.
In the 1890s, Americans advanced overseas expansion for economic, strategic, and ideological reasons. The first was economic. Some business leaders argued that factories produced more than Americans could buy, and the Panic of 1893 strengthened their case for foreign markets. The second was strategic. Alfred Thayer Mahan's The Influence of Sea Power upon History (1890) argued that great nations need steel navies and overseas bases, and Congress began building a modern fleet. The third was ideological. Social Darwinism and missionary zeal led many Americans to believe they had a duty to spread Christianity and "civilization."
Hawaii shows these motives working together. American planters and other residents, some hurt by the McKinley Tariff of 1890, organized the overthrow of Queen Liliuokalani in 1893. U.S. troops landed in Honolulu, helping the overthrow succeed. President Cleveland opposed annexation, but Congress annexed Hawaii under President McKinley in 1898, partly because of Pearl Harbor's value as a naval base.
In Asia, Secretary of State John Hay's Open Door notes (1899-1900) asked the European powers and Japan to keep China open to everyone's trade. In Latin America, Theodore Roosevelt helped Panama break away from Colombia in 1903 to secure land for the Panama Canal, which opened in 1914. His Roosevelt Corollary (1904) claimed the right to act as an "international police power" in the Western Hemisphere. Taft and Wilson later took different approaches to the region, compared in the table below.
Why did American sugar planters in Hawaii want annexation after 1890?
The McKinley Tariff made most foreign sugar duty-free and gave U.S. producers a bounty. Annexation offered Hawaiian planters a chance to receive the bounty and compete on the same terms.
| President | Policy name | Main tool | Example |
|---|---|---|---|
| Theodore Roosevelt (1901-1909) | Big Stick diplomacy | Threat of military force | Panama Canal zone (1903) and the Roosevelt Corollary (1904) |
| William Howard Taft (1909-1913) | Dollar diplomacy | U.S. investment and loans backed by the government | Marines sent to protect U.S. bankers' interests in Nicaragua (1912) |
| Woodrow Wilson (1913-1921) | Moral (missionary) diplomacy | Promoting governments Wilson considered legitimate, sometimes through military intervention | Occupation of Veracruz (1914) and Pershing's expedition into Mexico (1916) |
Cubans rose against Spanish rule in 1895. Spanish General Valeriano Weyler forced civilians into reconcentration camps, where tens of thousands died. Americans had about $50 million invested in Cuban sugar, and Hearst's and Pulitzer's newspapers ran exaggerated atrocity stories in a style called yellow journalism. In February 1898, the leaked de Lôme letter insulted President McKinley. Days later, the USS Maine exploded in Havana harbor and killed 266 sailors. The papers blamed Spain, but the cause remains disputed. An accidental coal bunker fire is one possible explanation.
Congress declared war in April 1898 and passed the Teller Amendment, which promised the U.S. would not annex Cuba. The war lasted under four months. Commodore George Dewey destroyed Spain's Pacific fleet at Manila Bay on May 1. On July 1, U.S. troops, including Roosevelt's Rough Riders and Black soldiers of the 9th and 10th Cavalry, took Kettle Hill and San Juan Hill near Santiago.
In the Treaty of Paris (December 1898), Spain gave up Cuba and ceded Puerto Rico, Guam, and the Philippines, with the U.S. paying $20 million for the Philippines. The Senate approved it in 1899 by just one vote more than the two-thirds needed. Filipinos led by Emilio Aguinaldo had expected independence, and the Philippine-American War (1899-1902) killed over 4,000 U.S. soldiers and an estimated 200,000 Filipino civilians. Cuba became independent on paper, but the Platt Amendment (1901) gave the U.S. the right to intervene there and a base at Guantánamo Bay.
How did the U.S. keep the Teller Amendment's promise while still controlling Cuba?
It did not annex Cuba, but the Platt Amendment of 1901 gave the U.S. the right to intervene in Cuban affairs and a naval base at Guantánamo Bay, making Cuba a protectorate.
When war broke out in 1914, Wilson declared neutrality, but American money flowed toward the Allies. By 1917, U.S. banks had loaned Britain and France over 27 million. German U-boats sank the British liner Lusitania in May 1915, killing 128 Americans. Germany then promised in the Sussex pledge of 1916 to stop sinking ships without warning. On February 1, 1917, it resumed unrestricted submarine warfare. Britain also passed along the Zimmermann Telegram. Germany proposed an alliance if the U.S. entered the war and promised to help Mexico recover Texas, New Mexico, and Arizona. Congress declared war on April 6, 1917.
The Selective Service Act (1917) drafted about 2.8 million men, and about 2 million Americans served in France under General John J. Pershing. They helped stop Germany's 1918 offensive and joined the Meuse-Argonne offensive before the armistice of November 11, 1918. About 116,000 Americans died, many from disease and the 1918 flu.
At home, Bernard Baruch's War Industries Board directed production, and Herbert Hoover's Food Administration promoted "meatless" and "wheatless" days. The Committee on Public Information produced propaganda. The Espionage Act (1917) and Sedition Act (1918) punished antiwar speech, and Eugene Debs got 10 years in prison. In Schenck v. United States (1919), the Supreme Court upheld these limits with its "clear and present danger" test. Hundreds of thousands of Black Southerners moved north during the Great Migration, often seeking factory jobs and an escape from Jim Crow. In East St. Louis in 1917, white mobs attacked Black residents amid racial hostility and competition over jobs. Women's war work helped win the 19th Amendment in 1920.
Germany sank the Lusitania in 1915, so why did the U.S. not declare war until 1917?
Germany limited its submarine attacks after U.S. protests and made the Sussex pledge in 1916. It resumed unrestricted submarine warfare on February 1, 1917, and the Zimmermann Telegram further increased support for entering the war.
In January 1918, Wilson laid out his Fourteen Points, which called for open diplomacy, freedom of the seas, free trade, arms reduction, greater self-government for some national groups, and a League of Nations. At the Paris Peace Conference in 1919, he negotiated with Britain's David Lloyd George, France's Georges Clemenceau, and Italy's Vittorio Orlando. France had been devastated and wanted Germany punished. Wilson gave up many of his points to keep the League in the treaty.
The Treaty of Versailles (June 28, 1919) included Article 231, the war guilt clause. It required reparations, later set at about $33 billion. It also capped Germany's army at 100,000 men, returned Alsace-Lorraine to France, and gave Germany's colonies to the Allies as League mandates. The broader postwar settlement recognized new states, including Poland, Czechoslovakia, and Yugoslavia. Many colonized peoples in Asia and Africa remained under foreign rule.
At home, the treaty needed a two-thirds Senate vote. Senator Henry Cabot Lodge wanted reservations, especially to Article 10, which he feared would commit U.S. troops to wars without approval from Congress. "Irreconcilables" like William Borah opposed the treaty entirely. Wilson toured the country to build support, then suffered a stroke in October 1919. He told Democrats to reject the Lodge version, so the treaty failed in November 1919 and again in March 1920. The U.S. never joined the League and made a separate peace with Germany in 1921. Warren Harding won in 1920 by promising a "return to normalcy."
Which part of the League of Nations covenant worried many senators, and why?
Article 10 worried them because its collective security promise seemed to commit the U.S. to defend other nations without a vote by Congress.
| Wilson's goal | What the treaty actually did |
|---|---|
| Peace without victory, with no harsh punishment of Germany | War guilt clause, about $33 billion in reparations, and strict military limits |
| Greater self-government for some national groups | New nations in Eastern Europe, but colonies became Allied mandates |
| Open diplomacy, with no secret deals | Major decisions made privately by the Big Four leaders |
| A League of Nations with U.S. leadership | League created, but the Senate rejected the treaty that would have brought the U.S. into it |
| Term | Definition |
|---|---|
| Imperialism | A policy of extending a nation's power over other lands through colonies, military force, or economic control. |
| Yellow journalism | Sensational, often exaggerated news reporting, used by Hearst and Pulitzer to stir up support for war with Spain. |
| Platt Amendment | The 1901 provision that let the U.S. intervene in Cuba and lease Guantánamo Bay, making Cuba a protectorate. |
| Anti-Imperialist League | An 1898 organization that opposed annexing the Philippines because it denied Filipinos self-government. |
| Roosevelt Corollary | Theodore Roosevelt's 1904 claim that the U.S. could act as a police power in Latin America to keep Europe out. |
| Unrestricted submarine warfare | Germany's policy of sinking any ship in a war zone without warning, which it resumed in January 1917 and which helped bring the U.S. into the war. |
| Espionage and Sedition Acts | Laws passed in 1917 and 1918 that punished interference with recruitment and specified forms of antiwar speech, including disloyal or abusive language about the government. |
| Great Migration | The large movement of Black Southerners to Northern cities beginning around World War I, in search of jobs and an escape from Jim Crow. |
| Self-determination | The principle that a people should choose its own government. Wilson supported greater self-government for some national groups in his Fourteen Points, but he did not apply the principle to all peoples. |
| League of Nations | The international organization created by the Treaty of Versailles to keep the peace, which the U.S. never joined. |
Newspapers in 1898 blamed Spain, so the claim sticks. Spain's responsibility was never proven. The cause remains disputed, and an accidental coal bunker fire is one possibility. What matters for the course is that the press used the explosion to push the country toward war.
The Lusitania went down in May 1915, but the U.S. declared war in April 1917. In between, Germany made and then broke the Sussex pledge. Connect the declaration of war to the resumption of unrestricted submarine warfare and the Zimmermann Telegram in early 1917.
The Fourteen Points were Wilson's 1918 wish list. The treaty was a compromise that punished Germany far more than Wilson wanted. You should also remember that the U.S. never ratified the treaty or joined the League, even though the League was Wilson's idea.
The Teller Amendment ruled out annexing Cuba, so Cuba became formally independent in 1902. The U.S. still controlled it through the Platt Amendment, which allowed intervention and created the base at Guantánamo Bay. The territories the U.S. actually took were Puerto Rico, Guam, and the Philippines.