1914

1. June 28 Assassination of Archduke of Austria-Hungary Franz Ferdinand
2. July 28 Austria-Hungary declares war on Serbia
3. August 1–4 Germany, Austria-Hungary, France, Russia, and Britain all commit to war
4. August 4 Germany invades Belgium; United States declares its neutrality

5. 

6. August 15 Panama Canal officially opens
7. August 23 Japan declares war on Germany
8. August 24 American poet Alan Seeger volunteers for French Foreign Legion; many individual Americans go to Europe and join both sides in the conflict
9. August 26 German forces burn Louvain, Belgium
10. August 25–30 Battle of Tannenberg in which Germany defeats Russia on the Eastern Front; more than 90,000 Russian soldiers surrender to German forces
11. September 5–10 First Battle of the Marne (France); at the time, the largest battle ever with one million soldiers on each side

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13. September Marie Curie becomes director of the Red Cross Radiology Services and begins leading an effort to set up France's first military radiology centers
14. September 14–October 14 24,000 soldiers from India arrive in France to fight for Allies
15. October 22 Herbert Hoover takes the helm of the Commission for Relief in Belgium
16. October 22–November 22 First Battle of Ypres; combat between German, British, and French forces bogs down into attritional trench warfare
17. October 29 Ottoman Empire attacks Russia
18. December 24 German planes make first air attack on Britain at Dover

1915

1. January 25 First official transcontinental telephone call
2. February 8 D. W. Griffith's film, later titled Birth of a Nation, premieres and sweeps the nation
3. May 7 Sinking of British ocean liner Lusitania by a German submarine results in nearly 1,200 deaths, 128 of which are American

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5. May 23 Italy enters war on Allied side
6. July 9 German South-West Africa (modern Namibia) surrenders to South Africa
7. July 17 British women demand equal rights to work in war industries
8. September 15 "Jelly Roll Blues" by Ferdinand "Jelly Roll" Morton is published; the piece later is called the "first jazz composition"
9. October 15 J. P. Morgan & Co. and other American bankers agree to loan Britain and France $500,000,000 to purchase war supplies; it is still the largest private loan floated in any country ever
10. October 23 More than 25,000 women, demanding the right to vote, march in New York City

11. 

12. November 25 Albert Einstein publicly presents his general theory of relativity
13. December 4 Henry Ford's Peace Ship sets sail to Europe; peace activists aboard seek an end to the war through mediation
14. December Allies evacuate from Gallipoli almost 83,000 men, many of these soldiers are from Australia and New Zealand; Ottoman victory boosts standing of future Turkish leader Mustafa Kemal Ataturk

1916

1. February 21 Battle of Verdun opens with German artillery assault deploying more than 1,600 artillery pieces and firing 100,000 shells per hour

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3. March 15 U.S. troops under the command of General John J. Pershing cross the border into Mexico in pursuit of Pancho Villa
4. April 16 American pilots form the Lafayette Escadrille in France
5. April 24 Easter Rising: more than 1,600 Irish nationalists rebel against British government; uprising results in 2,000 dead and its leaders executed
6. June 5 Arab Revolt against the Ottoman Empire begins with an uprising in Medina
7. July 1 Battle of the Somme begins; the conflict results in massive casualties: 419,000 for the British, 202,000 for the French, and as many as 600,000 for the Germans
8. July 30 Explosion in New Jersey set by German saboteurs destroys the Black Tom munitions depot, resulting in 3 dead and more than 30 million dollars in damages

9. 

10. September 15 Britain first uses the tank in battle at the Somme
11. November 7 Woodrow Wilson, campaigning on the slogan "He kept us out of war," barely wins the presidential election of 1916
12. November 18 Battle of the Somme ends after four and a half months
13. December 18 The nine-month-long Battle of Verdun ends; French African troops contribute to fighting at Verdun; by the end of the war, 450,000 soldiers from France's African colonies serve in combat

1917

1. February 1 Germany resumes unrestricted submarine warfare; submarines threaten all shipping to Britain, endangering U.S. trade and travelers
2. February 20 Food riots begin in New York City and spread to other cities, as several hundred female protesters grow angry over sharp jumps in food prices due to the war
3. March 1 White House releases Zimmermann telegram to the press, exposing Germany's attempt to draw Mexico into war against the United States
4. March 15 Tsar Nicholas II abdicates during the Russian Revolution and is replaced by a provisional government

5. 

6. April 6 U.S. declares war on Germany
7. April 24 Emergency Loan Act passes; U.S. begins First Liberty Loan Bond Campaign to fund war efforts, to be followed by four other bond drives
8. May 18 Selective Service Act passes, which enabled the U.S. to form its first army derived largely from conscription

9. 

10. June 15 Congress passes Espionage Act, which limits civil liberties during wartime
11. June 26 U.S. 1st Division (approximately 14,000 soldiers) of the American Expeditionary Forces (AEF) lands in France, the first American combat troops to arrive in Europe
12. June 28 "Over There" by George M. Cohan is recorded
13. July 2 East St. Louis Race Riots: pressures arising from the movement of blacks north during the Great Migration results in violence as white residents attack their African American counterparts who attempt to defend themselves from attack
14. July 6 Arab forces aligned with the Allies seize the port of Akaba on the Red Sea
15. July 28 Silent Parade: 10,000 African Americans march in New York City to protest lynching, specifically the violence of the East St. Louis Riots
16. August 28 Ten suffragists are arrested protesting outside the White House
17. October 21 U.S. troops enter the frontline trenches in France for the first time
18. November 2 Balfour Declaration is issued in London, giving British support for establishing a Jewish homeland in Palestine
19. November 7 Bolsheviks led by Vladimir Lenin seize power from the Provisional Government in Russia
20. November 10 Battle of Caporetto ends with a disastrous Italian retreat
21. December 7 U.S. declares war on Austria-Hungary to prevent Italy from leaving war
22. December 17 Congress passes prohibition amendment to the U.S. Constitution

1918

1. January 8 Woodrow Wilson delivers his "Fourteen Points" address
2. January 9 Wilson announces his support for a constitutional amendment to grant women the right to vote
3. February 8 U.S. armed forces newspaper The Stars and Stripes begins publication

4. 

5. March 3 Russia's Bolshevik government signs the Brest-Litovsk Treaty with Germany; Russia leaves the war but loses roughly 1/2 of its industry, 1/3 of its farmland, and 1/3 of its population
6. March 4 First U.S. soldiers are reported ill with influenza at Camp Funston in Kansas; the global epidemic will claim more lives than the war itself with more than 30 million of the global population succumbing to the pandemic
7. March 21 German spring offensives begins; this series of German attacks on the Western Front will strain Allies almost to the breaking point
8. March 26 In the U.S. Senate, it is admitted that the United States will have 37 aircraft ready for the AEF by July, rather than the 12,000 that had been promised
9. March 31 U.S. initiates Daylight Savings Time
10. April 21 The "Red Baron" Manfred von Richthofen is shot down and killed
11. April 21 Guatemala at war with Germany
12. May 16 Sedition Act of 1918; extends provision of the Espionage Act and further limits free speech
13. June Civil war in Russia erupts
14. June 6 Battle of Chateau-Thierry; U.S. Marines launch attack at Belleau Wood
15. July 15–17 Second Battle of the Marne; French and U.S. forces stop German advance on Paris
16. July 16–17 Bolsheviks execute Tsar Nicholas II and his family
17. August 10 U.S. First Army organized; U.S. now has an independent fighting force in France capable of conducting large-scale offensives

18. 

19. August 16 First U.S. soldiers arrive in Vladivostok, Russia's Siberian port; these occupying forces eventually grow to 9,000
20. September 4 4,500 U.S. soldiers land in Archangel, North Russia
21. September 12–16 Battle of St. Mihiel; first U.S. led offensive in World War I proves largely successful
22. September 14 Socialist leader Eugene Debs is sentenced to ten years imprisonment for violating the Espionage Act by giving an anti-war speech.
23. September 26 Meuse-Argonne Offensive begins; the battle in which more Americans were killed than in any battles of the Civil War or World War II
24. October 6 Germany requests armistice; Allies refuse request
25. October 28 Czechoslovakia declares independence from Austria-Hungary
26. October 30 Ottomans agree to armistice
27. October 31 In one week, influenza virus kills 21,000 in the United States
28. November 3 Austria-Hungary agrees to armistice
29. November 9 Germany's Kaiser Wilhelm II leaves for exile in the Netherlands
30. November 11 Armistice with Germany

31. 

32. December 1 Allies begin occupying Germany's Rhineland region; W. E. B. Du Bois sails for France to begin organizing the First Pan African Conference
33. December 13 Woodrow Wilson arrives in Paris for peace conference; he becomes the first serving president to travel to Europe

1919

1. January 18 Paris Peace Conference begins
2. January 19 18th Amendment on prohibition ratified

3. 

4. March 3 In Schenck v. U.S., the Supreme Court rules free speech may be limited during wartime, notably when it presents a "clear and present danger"
5. June 4 Congress approves the 19th Amendment on women's right to vote
6. June 28 Germany and Allies sign Treaty of Versailles
7. July 27 – August 3 Chicago Race Riots: arising from the pressures of the Great Migration, white mobs attack African Americans and African Americans fight back, 15 whites and 23 blacks perish in riot, illustrative of a series of riots across the nation including Washington, D.C., referred to as "Red Summer"

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9. September 3 Woodrow Wilson begins his tour of the U.S. to promote the Treaty of Versailles; later, on tour, he collapses from his efforts
10. November 19 U.S. Senate refuses to ratify the Treaty of Versailles

1920

1. January 16 League of Nations holds its first meeting
2. August 18 – 19 Amendment on women's suffrage ratified

3. 

1921

1. August 25 Peace treaty signed between U.S. and Germany