Book excerpt: The first half of the 20th century was perhaps the most turbulent in history. Two world wars and numerous smaller conflicts significantly changed the geopolitical map, resulting in an unprecedented number of changes throughout the world. Some of the leaders in the period made an indelible mark on their nation and, in some cases, the world; others are scarcely remembered even in their own homeland. Nearly 1,200 emperors, kings, queens, presidents, prime ministers, premiers, emirs, and other heads of state or government served from 1900 through 1945, and all are included in this comprehensive reference work. Each biographical profile first gives birth and death dates, then gives an account of how the leader came to power and an overview of his or her term in office. The profiles are packed with data.