What is International Economic Law?

Before answering this question, let us consider the following: What is the legal relationship when Chinese Government purchase United States treasury bonds? If a dispute arises, what dispute resolution procedures apply, litigation or arbitration, domestic or international? What is the legal basis for settlement, international law or domestic law, and if domestic law, is it U.S. law or Chinese law? As the Government that is the subject of the transaction, in what capacity, in what way, and in what place did China purchase the treasury bonds, is it exercising a sovereign act or engaging in a commercial act, and what kind of responsibility should it bear? Is it a matter of civil law or administrative law or constitutional law? Is it a matter of public international law or international economic law?