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The assassination, carried out by Gavrilo Princip in Sarajevo, led Austria-Hungary to issue an ultimatum to Serbia, and Austria-Hungary's subsequent declaration of war against Serbia on July 28, 1914, activated a system of European alliances that drew other major powers into the conflict. -
was the official U.S. policy to remain out of the European conflict. Despite this stance, American neutrality was challenged by factors like financial ties to the Allies, German submarine warfare, and German attempts to draw the U.S. into the war via actions like the Zimmermann Telegram. -
a crucial Allied victory that halted the German advance on Paris during World War I, ending Germany's hope for a quick victory and initiating four years of brutal trench warfare. -
On May 7, 1915, the German submarine U-20 torpedoed and sank the British ocean liner Lusitania off the coast of Ireland. The attack killed 1,198 of the 1,959 people on board, including 128 Americans, in under 20 minutes. -
The Battle of Verdun was a 10-month-long World War I battle in 1916 where the French repulsed a major German offensive, resulting in hundreds of thousands of casualties on both sides. -
torpedoing of a French cross-Channel passenger steamer, the Sussex, by a German submarine, leaving 80 casualties, including two Americans wounded. The attack prompted a U.S. threat to sever diplomatic relations. -
was a battle of the First World War fought by the armies of the British Empire and the French Republic against the German Empire. It took place between 1 July and 18 November 1916 on both sides of the upper reaches of the river Somme in France. -
The Zimmermann telegram was a secret diplomatic communication issued from the German Foreign Office on January 17, 1917, that proposed a military contract between the German Empire and Mexico if the United States entered World War I against Germany. -
a World War I naval tactic to sink any ship, including passenger vessels, in the waters around Britain to disrupt supply lines and starve Britain into submission. -
Key factors included Germany's unrestricted submarine warfare, the sinking of the Lusitania, and the interception of the Zimmermann Telegram, which revealed a German plot to ally with Mexico against the U.S. President Woodrow Wilson requested the declaration of war from Congress, arguing the world must be made "safe for democracy". -
established the modern draft system for the U.S. military. -
a U.S. federal law enacted in 1917 that prohibits the unauthorized disclosure of national defense information, aiming to prevent it from being used to harm the United States or aid a foreign power. -
the U.S. Army's fighting force during World War I, commanded by General John J. Pershing. -
a set of principles he proposed in January 1918 for achieving lasting peace after World War I, emphasizing open diplomacy, free trade, disarmament, and national self-determination. -
Estimates of deaths range from 17 million to 50 million, and possibly as high as 100 million, making it the deadliest pandemic in history. -
Russia officially pulled out of World War I by signing the Treaty of Brest-Litovsk with the Central Powers on March 3, 1918, after the Bolshevik Revolution of 1917. The withdrawal was driven by the war's immense losses, economic collapse, and the new Bolshevik government's goal of securing peace to focus on internal consolidation. -
used to suppress dissent during World War I and was later deemed by modern scholars to violate core free speech protections. -
It was fought from September 26, 1918, until the Armistice of November 11, 1918, a total of 47 days. -
on November 11, 1918, marked the end of fighting in World War I, not the official end of the war. At 11:00 a.m. on that day, a ceasefire went into effect after Germany signed an armistice with the Allies. The treaty that officially concluded the war, the Treaty of Versailles, was not signed until June 28, 1919. -
a 1919 meeting where Allied powers negotiated the terms for peace after World War I.