This book is written in homage Pierre Hassner, one of the great thinkers on the question of violence and peace. It contains contributions from his philosophical followers in International Relations. Its value lies in the fact that it provides a key to an understanding of the 21st century and a key to a rereading of the 20th century, in support of the great philosophers from Machiavelli to Kant. The contributions are by some of the best thinkers in political philosophy and international studies, both French and international.