Between 1914 and the spring of 1917, the European nations engaged in a conflict that became known as World War I. While armies moved across the face of Europe, the United States remained neutral. In 1916 Woodrow Wilson was reelected President for a second term, largely because of the slogan "He kept us out of war."

Events in early 1917 would change that hope. In frustration over the effective British naval blockade, Germany broke its pledge to limit submarine warfare on February 1, 1917. In response to the breaking of the Sussex pledge, the United States severed diplomatic relations with Germany. Several weeks later, on February 24, the British presented the Zimmermann telegram to the U.S. Government in an effort to capitalize on growing anti-German sentiment in the United States. The American press published news of the telegram on March 1. On April 6, 1917, the United States Congress formally declared war on Germany and its allies.

The Zimmermann Telegram had such an impact on American opinion that, according to David Kahn, author of The Codebreakers, "No other single cryptanalysis has had such enormous consequences." It is his opinion that "never before or since has so much turned upon the solution of a secret message.

This text was adapted from the article "The Zimmerman Telegram" by Mary Alexander and Marilyn Childress. Citation: Alexander, Mary and Marilyn Childress. "The Zimmerman Telegram." Social Education 45, 4 (April 1981): 266