Final answer:
Trade obstacles are legal forces created through the passage of laws or the negotiation of international trade agreements. They protect the interests of certain industries or nations by imposing barriers like tariffs or quotas on foreign products.
Step-by-step explanation:
Trade obstacles are considered to be legal forces because they are created through the passage of laws or the negotiation of international trade agreements. These laws and agreements are designed to protect the interests of certain industries or nations by imposing barriers such as tariffs or quotas on certain foreign products. For example, a country may pass a law to protect its domestic industries from competition by imposing a tariff on imported goods. This creates a legal barrier that prevents or discourages foreign products from entering the market.