President Woodrow Wilson promised that American intervention into World War I would "make the world safe for democracy." But his dreams of a stable, democratic postwar order collapsed when Americans rejected the Treaty of Versailles and refused to join the League of Nations.
The First World War quickly devolved into a prolonged stalemate along the heavily entrenched Western Front. Millions of men died in futile efforts to capture the few hundred yards of territory that separated the opposing armies across "No Man's Land."
The death toll from trench warfare was horrific. In the 1916 Battle of the Somme, the British Army suffered nearly 60,000 casualties on a single day.
World War I soldiers regularly endured chemical weapons attacks, donning gas masks in hopes of surviving barrages of poison mustard gas.