This book, finished in September 2023, addresses the fundamental principles enshrined in Resolution 2625 (XXV): sovereignty, the principle of non-intervention, the prohibition of the use of force, and self-determination. Studying these principles can help us understand some of the main features of international law and the international community in the 21st century: the role of traditional and new subjects alike; the sources of international law; issues of international responsibility; and new international challenges. For this purpose, the book analyses in each chapter the main...