Step 1: Historical background.
The book “Droit des Gens” (The Law of Nations) was published in 1758. It is one of the most influential works on international law.
Step 2: Author.
It was written by Emerich de Vattel, a Swiss jurist. His work shaped modern concepts of state sovereignty and diplomacy.
Step 3: Conclusion.
Thus, the correct answer is (b).