Final answer:
Nations promote exports while restricting imports through various measures like tariffs, quotas, and bans to protect national interests such as industry, security, jobs, and the environment.
Step-by-step explanation:
For centuries, nations have combined two opposing policy attitudes toward the movement of goods across national boundaries. On one hand, nations promote exports; on the other hand, the flow of imports can be restricted. This can be seen in various policies that nations employ, such as the imposition of tariffs, quotas, and outright bans on certain goods to protect their national interests, including safeguarding critical industries, preserving jobs, ensuring national security, and maintaining environmental standards.
Nation X and nation Y may be geopolitical rivals, and if nation Y has a comparative advantage in a critical area like missile defense systems, it is unlikely to export those to nation X. Similarly, if foreign governments subsidize the production of certain goods, this may lead to an increase in imports for countries like the United States, where domestic companies might find it cheaper to purchase goods like steel from abroad, despite the potential threats to national security or environmental protection laws.