Why do nations trade and specialize?

"One might argue that the best way to protect workers and the domestic economy is to stop trade with other nations. Then the whole circular flow of inputs and outputs would stay within our borders. But if we decided to do that, how would we get resources like cobalt and coffee beans? The United States simply can’t produce some things, and it can’t manufacture some products, such as steel and most clothing, at the low costs we’re used to. The fact is that nations—like people—are good at producing different things: you may be better at balancing a ledger than repairing a car. In that case you benefit by “exporting” your bookkeeping services and “importing” the car repairs you need from a good mechanic. Economists refer to specialization like this as advantage. A country has an absolute advantage when it can produce and sell a product at a lower cost than any other country or when it is the only country that can provide a product. The United States, for example, has an absolute advantage in reusable spacecraft and other high-tech items. Suppose that the United States has an absolute advantage in air traffic control systems for busy airports and that Brazil has an absolute advantage in coffee. The United States does not have the proper climate for growing coffee, and Brazil lacks the technology to develop air traffic control systems. Both countries would gain by exchanging air traffic control systems for coffee."