How does comparative advantage encourage free trade?

"Even if the United States had an absolute advantage in both coffee and air traffic control systems, it should still specialize and engage in trade. Why? The reason is the principle of comparative advantage, which says that each country should specialize in the products that it can produce most readily and cheaply and trade those products for goods that foreign countries can produce most readily and cheaply. This specialization ensures greater product availability and lower prices. For example, India and Vietnam have a comparative advantage in producing clothing because of lower labor costs. Japan has long held a comparative advantage in consumer electronics because of technological expertise. The United States has an advantage in computer software, airplanes, some agricultural products, heavy machinery, and jet engines. Thus, comparative advantage acts as a stimulus to trade. When nations allow their citizens to trade whatever goods and services they choose without government regulation, free trade exists. Free trade is the policy of permitting the people and businesses of a country to buy and sell where they please without restrictions. The opposite of free trade is protectionism, in which a nation protects its home industries from outside competition by establishing artificial barriers such as tariffs and quotas. In the next section, we’ll look at the various barriers, some natural and some created by governments, that restrict free trade."