The transatlantic telegraph and steam powered ocean transit made the world quite a bit smaller, and brought about the first period of true globalization. For the first time the events across the globe could be read at the breakfast table by ordinary Americans in great detail and relatively soon after they happened. The Zimmerman Telegram and Unrestricted Submarine Warfare by Germany meant that actions by other nations directly affected ordinary Americans. In 1914, the majority of Americans wanted to stay neutral in the latest iteration of the four hundred years long Franco-German struggle for dominance of continental Europe. Less than three years later, the majority of Americans were for intervention.
On 2 April 1917, President Woodrow Wilson broke his campaign promise to “Keep us out of the war” and asked Congress to declare war on Imperial Germany in order to go to “war to end war” and, “The world must be safe for democracy”. On 4 April the Senate voted to declare war and at 3 am on 6 April 1917, the House of Representatives followed suit. That day, President Wilson announced that America had entered the Great War.
The United States was woefully unprepared. The US Army, to include the entire National Guard, was only 208,000 strong. They had just 10,265 men in the US Marine Corps. More Frenchmen and British had been killed (much less wounded) at Verdun and the Somme just the year before than existed in the entire US military. The American army had little experience with units over the size of a regiment since the US Civil War, fifty years before. The War Department had no experience, infrastructure, staff, or plans for the millions of Americans that would need to be drafted in order to stabilize the Western Front.
Nonetheless, the first Americans headed “Over there” in less two months.
The Spanish American War might have introduced us to the World Stage, but now we were starring on it, and would continue to so for the next century. But at the time, we didn’t even know our lines.