The United States had had a policy of neutrality since its inception in the late eighteenth century. Thomas Jefferson, the third president, had warned the country of the dangers of "entangling alliances" in 1801. To counter this deep-seated tradition, the US government engaged in a propaganda campaign to win support for American participation in World War I (1914–1918).
Germany and Britain attempted to interfere with each other's commerce on the high seas during WWI. Because the British fleet was the most powerful in the world, the Germans had to rely on submarines to fight back. In 1915, the Germans sank the Lusitania. Over one hundred Americans died, and former President Theodore Roosevelt asked the current President, Woodrow Wilson, to declare war. Not ready for that, Wilson protested to the Germans and prepared the country for war. Also, the US government's public blaming of Germany was an effort to change public opinion. In fact, the Lusitania was illegally carrying munitions and Americans had been warned not to sail on the ship.
Wilson won reelection in 1916 in part because he kept the US out of the war, but American neutrality ended in 1917. Wilson tried to rally public support by claiming that America and her allies were fighting for democracy. There were Uncle Sam posters encouraging enlistment; posters exhorting the public to buy war bonds were ubiquitous. Wilson secured support from women, at least in part, by promising that women would soon be able to vote.
Propaganda was spread by the Committee on Public Information. This office was run by a former newspaper reporter, George Creel. He used modern propaganda techniques and hired tens-of-thousands of speakers to travel around the nation and rally support. A propaganda film, The Beast of Berlin, was released to public acclaim. Sauerkraut became known as "liberty cabbage," and schools stopped offering courses in German.
The U.S. government insisted that American citizens support the war effort. Dissent was not tolerated, and more than one thousand people were convicted under the Sedition and Espionage Acts. Surprisingly, the US Supreme Court upheld the legality of these draconian measures after the war in two 1919 cases.