The last hundred years have witnessed the ongoing decline of Europe’s population and the explosion of Africa’s, major changes in migratory flows, significant variations in fertility levels across different countries and ethnic groups and the dizzying growth of large metropolises. These changes alter and sometimes disrupt relations between societies, states and regions of the world and influence political choices, with variable and often unpredictable force and speed. Past and current crises, such as the difficulties faced by governments seeking to control immigration and to manage tensions between religious and ethnic communities, now appear as the inevitable consequence of these demographic changes. Geodemography – the study of how population dynamics influence societies, states and regions and affect the relations between them, over time and throughout the world – can help us to understand these trends. Using a broad repertoire of exemplary cases drawn from recent world history, this book demonstrates that geodemography is an invaluable tool for gaining a deeper appreciation of the changing relations between societies and states and the great challenges we face today.