Which law includes the study of treaties and international agreements?

The correct answer is International law because this area of law specifically addresses the rules, agreements, and treaties that govern relations between nations. International law encompasses a range of issues including human rights, trade, environmental regulations, and the conduct of war, making its focus on treaties and agreements between countries fundamental. International treaties, which are formal agreements recognized under international law, play a crucial role in facilitating cooperation and regulating interactions among states at a global level. In this context, the study of treaties is central to understanding how countries establish obligations and rights under international commitments, thus playing a vital role in the framework of international relations.

The other areas of law—civil, criminal, and constitutional—do not primarily concern themselves with the relationships and agreements between nations, thereby making them less relevant to the study of treaties and international agreements.