The Zimmermann Telegram by Barbara Wertheim Tuchman

A concise, narrative account of the 1917 German diplomatic proposal to Mexico and the chain of intelligence, diplomatic and propaganda events that followed after British cryptographers intercepted and deciphered it; the book reconstructs the decoding by British intelligence, the difficult decision to disclose the telegram, and the diplomatic and public reaction in the United States and Mexico, showing how that one diplomatic gamble—combined with submarine warfare—helped shift U.S. opinion and policy and played a pivotal role in bringing the United States into World War I.