Answer: Act of State Doctrine
Explanation: The Act of State Doctrine is a principle of International law that prevents courts from questioning the validity of a foreign country's sovereign acts that take place within its own territory and that courts should not decide cases that would interfere with their country's foreign policy. It then follows that every sovereign state is bound to respect the independence of other sovereign states. Nation B therefore cannot meddle with Nation A’s decision under the Act of State Doctrine.