On May 7, 1915, a German submarine torpedoed the British passenger liner Lusitania that was en route from New York City to London. Attacked without warning, the ship sank in fifteen minutes, killing 1,198 civilians, including 128 American men, women and children.
Woodrow Wilson immediately denounced the sinking of the Lusitania in harsh, threatening terms and demanded that Germany pledge to never launch another attack on citizens of neutral countries, even when traveling on French or British ships. Germany initially acquiesced to Wilson's demand but only temporarily. In March of 1916, a German U-boat torpedoed the French passenger liner Sussex, causing a heavy loss of life and injuring several Americans.
Two months later, in what is known as the Sussex pledge, German officials announced that they would no longer sink Allied merchant ships without warning. At the same time, however, they made it clear that it would resume submarine attacks if the Allies refused to respect international law, which in effect meant that the Allies had to lift their blockades of food and other raw materials bound for the Central powers.
Despite further provocations, President Wilson still hoped for a negotiated settlement until February 1, 1917, when Germany resumed submarine warfare against merchant ships, including those of the United States and other neutral countries. In response, Wilson immediately broke off diplomatic relations with Germany.
Then, on February 25, the British intercepted and decoded a telegram from Germany's foreign secretary Arthur Zimmermann to the German ambassador in Mexico. The so-called "Zimmermann telegram" proposed that in the event of war with the United States, Germany and Mexico would form an alliance. In return, Germany promised to regain for Mexico its "lost provinces" of Texas, Arizona, and New Mexico.
The release of the Zimmermann Telegram ignited a public furor that was further enflamed by the loss of at least three U.S. merchant ships to German submarines. All hope for neutrality was now lost, and, on April 2, 1917, Wilson appeared before a joint session of Congress and asked for a Declaration of War against Germany.
This is a partial excerpt of what he said:
It is a fearful thing to lead this great peaceful people into war, into the most terrible and disastrous of all wars, civilization itself seeming to be in the balance. But the right is more precious than peace, and we shall fight for the things which we have always carried nearest our hearts - for democracy, for the right of those who submit to authority to have a voice in their own governments, for the rights and liberties of small nations, for a universal dominion of right by such a concert of free peoples as shall bring peace and safety to all nations and make the world itself at last free. To such a task we dedicate our lives and our fortunes...
Wilson was having lunch in the State Dining Room of the White House when he received word that the Declaration of War had arrived for his signature. Although no one knows what Wilson ate for lunch on that momentous day, we do know that by the time the United States entered the war, German submarines were taking a devastating toll on the supplies of food and other provisions being shipped to Britain from abroad.
In response, the British admiralty decided to establish a system of convoys. Under the plan, merchant ships were grouped together in "convoys" and provided with warship escorts through the most dangerous stretches of the North Atlantic. The convoys had a dramatic effect. By the end of 1917, the tonnage of Allied shipping lost each month to German U-boat attacks plummeted from one million tons in April to about 350,000 tons in December.
And although many other critical factors were at play, the increase in food and other necessary wartime provisions helped to stiffen the resolve of French and British troops and thwarted Germany’s attempt to force Britain’s surrender.