World War I was a brutal war that left more than 9 million dead. Millions more were wounded and lost their homes. The two sides—the Allied Powers and Central Powers—cut secret deals to get countries to join their side. They unleashed secret weapons, employed spies, and relied on the element of surprise itself to wage terrible battles. Secrets of World War I reveals little-known stories of the people, weapons, and battles that have affected the maps on our walls and the allegiances in our hearts.