World War I was an epic conflict that toppled centuries-old empires, transformed the Middle East and Russia, and helped elevate the United States to prominence as a world power. In essence, understanding the reasons for and outcomes of the First World War provides a cornerstone for knowledge of all modern history. In , detailed reference entries, a comprehensive overview essay, plus additional examinations of the causes and consequences of the conflict provide readers with the context needed to understand all aspects of World War I. Important primary source documents like the Zimmerman Telegram and Balfour Declaration are included and accompanied by explanations that supply readers with key historical perspective. Biographies on major political and military leaders, such as Wilhelm II, Woodrow Wilson, Nicholas II, John Pershing, and Ferdinand Foch, offer insight into the people who played key roles in the conflict. Entries on the key confrontations of the war—many accompanied by maps—showcase the strategies of both sides in their attempts to emerge victorious, and the bibliography presents a wealth of options to students looking to conduct further research on World War I.