Chapter 9 — International Trade

Comparative Advantage in a Global Economy

Chapter 3 introduced comparative advantage with a worked example of two roommates trading meals and laundry. Now we scale the same logic up to countries. The mechanism is identical — different opportunity costs, mutual gains from specialization and trade — but the consequences are larger, the politics is harder, and the empirical record includes some genuinely difficult cases that the simple model doesn't fully capture.

This chapter has three jobs. First, it shows you how the supply-and-demand framework from Chapters 5–8 applies to international trade. You'll learn how to draw a tariff diagram, identify who gains and who loses, and calculate the welfare effects using the surplus framework from Chapter 8. Second, it gives you the standard economic case for free trade — which is real, well-supported, and widely held among professional economists. Third, and this is the part that distinguishes this chapter from a Mankiw treatment: it takes seriously the case against free trade as it has actually been practiced, including the empirical work on the "China shock" and the very real damage that trade liberalization has caused in some American communities.

By the end, you should be able to do the standard analysis cleanly and also articulate why free trade is more contested politically than the standard analysis would suggest. This is an honest version of the trade story — one that economists who study trade increasingly endorse, even though many introductory textbooks still present trade as if everyone benefits and no one is meaningfully hurt.

The chapter has six sections. Section 1 reviews comparative advantage at the country level. Section 2 introduces the tariff diagram and the surplus calculation. Section 3 covers quotas and other trade restrictions. Section 4 walks through the China shock. Section 5 covers the political economy of trade. Section 6 closes with what economic analysis can and cannot tell you about trade policy.

9.1 Comparative advantage at the country level

Recall the two-roommate example from Chapter 3. Anna and Ben had different opportunity costs of producing meals and laundry. By specializing in their lower-opportunity-cost good and trading at a rate between their two opportunity costs, both ended up better off than they would have been alone. The result was true even though Anna was better at both tasks (absolute advantage in everything) — because comparative advantage, not absolute advantage, determines who should produce what.

Now imagine the same logic at the country level. The U.S. and China are the two "roommates." Each can produce many goods. In some, the U.S. has a lower opportunity cost (advanced semiconductors, software, aircraft, agricultural commodities like corn and soybeans). In others, China has a lower opportunity cost (consumer electronics assembly, textiles and apparel, certain metals and chemicals). When the two countries trade — exporting what they produce at low opportunity cost, importing what they could only produce at higher cost — both end up consuming more goods than either could have produced alone.

The total wealth of the two-country system grows. Output expands beyond what each country could have achieved in isolation. This is the gains-from-trade result, and it's as well-supported as any result in economics.

A worked example with countries

Suppose the United States can produce, in one labor-hour, either: - 4 units of soybeans, or - 1 unit of textiles

And China can produce, in one labor-hour, either: - 1 unit of soybeans, or - 1 unit of textiles

Absolute advantage: The U.S. has an absolute advantage in soybeans (4 vs. 1). Neither has an absolute advantage in textiles (both can produce 1).

Comparative advantage: - U.S. opportunity cost of 1 soybean = 0.25 textiles (giving up 0.25 textiles to make a soybean) - U.S. opportunity cost of 1 textile = 4 soybeans - China opportunity cost of 1 soybean = 1 textile - China opportunity cost of 1 textile = 1 soybean

The U.S. gives up less to produce soybeans (0.25 textiles vs. China's 1 textile). The U.S. has comparative advantage in soybeans.

China gives up less to produce textiles (1 soybean vs. U.S.'s 4 soybeans). China has comparative advantage in textiles.

Specialization and trade: If the U.S. specializes in soybeans and China specializes in textiles, and they trade at any ratio between 1:0.25 and 1:1 (soybeans per textile), both countries gain. The U.S. ends up consuming both more soybeans and more textiles than it could have produced alone. China does too.

The mechanism is the same as Chapter 3. What's new is that now the "trading partners" are entire countries, the goods are produced by millions of workers, and the political consequences of specialization are large. When the U.S. specializes in soybeans, that means American textile workers eventually find jobs in soybean farming or elsewhere — not in the textile factories that closed. When China specializes in textiles, that means Chinese soybean farmers (or those who would have been) find jobs in textile factories. Both transitions involve human beings whose lives change.

We will return to this in §9.4 (the China shock).

9.2 The tariff diagram

A tariff is a tax on imports. Like any tax, it raises the price of the affected good for buyers and lowers it for sellers. Unlike a domestic tax, though, a tariff has international consequences — it changes who produces, who exports, who imports, and how the gains from trade are distributed.

Let's draw the picture. Suppose the U.S. is a small importer of textiles, meaning the world price of textiles is determined by world supply and demand and the U.S. is a small enough buyer that it doesn't affect the world price.

                Tariff on Imported Textiles

   Price
        |  Demand              U.S. Domestic
        |                      Supply
   $25  |                       /
        |                      /
   $20  |                     /
        |                    / ← U.S. domestic supply
   $15  |═══════════════════════════ ← New world price + tariff ($15)
        |                  /
   $10  |═══════════════════════════ ← World price ($10)
        |                /
        |               /
   $ 5  |              /
        |             /
        |____________________________
        0    QD1 QD2  QS1  QS2     Quantity
              (with  (without
               tariff) tariff)

Figure 9.1 — A tariff on imports. Without a tariff, the world price prevails at $10. U.S. domestic supply provides QS1 units; U.S. demand wants QD1 units; the difference is imports. With a tariff of $5, the new effective price for U.S. buyers is $15. U.S. domestic supply rises to QS2 (more domestic production); U.S. demand falls to QD2 (less consumption); imports shrink. The tariff transfers welfare from consumers to domestic producers and the government, and creates a deadweight loss.

What does this picture tell us? Let's compute the surplus changes step by step.

Without the tariff (free trade at world price $10): - Consumer surplus is the area below the demand curve and above $10 - Producer surplus is the area above the U.S. domestic supply curve and below $10 (limited to the small quantity domestic producers actually supply at this price) - Imports are the difference between what consumers want at $10 and what domestic producers supply at $10

With the tariff (price $15): - Consumer surplus shrinks (consumers pay more, consume less) - Domestic producer surplus grows (producers receive more, produce more) - Government collects tariff revenue ($5 × quantity of imports) - There are two deadweight loss triangles

The two deadweight loss triangles are: 1. Production loss: domestic producers expand from QS1 to QS2, but they're producing at a higher cost than the world price would dictate. The triangle between the supply curve and the world price represents the inefficient extra production — units that could have been imported more cheaply. 2. Consumption loss: domestic consumers reduce their consumption from QD1 to QD2. The triangle between the demand curve and the new effective price represents trades that would have happened at the world price but don't happen with the tariff.

Both triangles are deadweight losses. They are value destroyed by the policy that no party (buyers, sellers, or government) captures.

The overall welfare effect: consumers lose more than producers gain. The government collects revenue but less than the consumer loss minus the producer gain. The net effect is negative — the tariff destroys welfare for the importing country as a whole.

This is the standard economic case against tariffs. It's mathematically rigorous and empirically defensible. It's also the case that 80–90% of leading economists endorse on the IGM Forum surveys.

9.3 Quotas and other trade restrictions

A quota is a quantity restriction on imports — only X units of a good can be imported per year, regardless of demand. The effects are similar to a tariff, but with one important difference: instead of the government collecting revenue, the quota holders (the firms allowed to import) capture the surplus that would have been tariff revenue.

This makes quotas worse than tariffs, from a national welfare perspective, because the surplus that would have been government revenue is instead a private gift to the quota holders (who, if they're foreign exporters, receive it abroad — meaning the importing country loses the revenue entirely). Most economists prefer tariffs to quotas for this reason.

Other trade restrictions include: - Voluntary export restraints (VERs): foreign exporters "voluntarily" limit their exports to avoid harsher restrictions. Economically, similar to quotas. The 1980s Japanese auto VERs are a famous example. - Anti-dumping duties: tariffs imposed when foreign producers are accused of selling below cost. Often used as protection in disguise. - Countervailing duties: tariffs imposed when foreign producers are accused of receiving subsidies from their home governments. - Non-tariff barriers: standards, labeling requirements, sanitary regulations, and other rules that effectively limit imports without being formally trade restrictions.

All of these have similar surplus effects in the basic framework, though the details differ.

9.4 The China shock

So far, this chapter has presented the standard economic case for free trade. It's a strong case, and most economists endorse it. But the case has a serious empirical complication that emerged in the 2010s: the work of David Autor, David Dorn, and Gordon Hanson on the "China shock."

The China shock refers to the rapid expansion of trade with China between roughly 2000 and 2010. Two events triggered it: China's accession to the World Trade Organization (WTO) in 2001, which formally locked in lower tariffs and gave Chinese exporters more secure access to world markets; and a sustained productivity boom in Chinese manufacturing that made Chinese goods even more competitive than the standard model would have predicted.

The result was an enormous surge in Chinese imports to the United States — particularly in manufactured goods like furniture, textiles, electronics, and certain metal products. The surge was concentrated in specific industries, in specific U.S. communities, and over a relatively short period. Autor, Dorn, and Hanson studied the consequences carefully.

What they found

Their core findings (summarized from their 2013, 2016, and 2020 papers):

1. The aggregate gains from trade with China were real. U.S. consumers benefited from cheaper goods. The standard surplus framework correctly identifies these gains.

2. The local labor-market damage was much larger than economists had predicted. Communities heavily exposed to Chinese import competition (places where the local economy was dominated by industries that competed directly with Chinese exports) experienced: - Sharp declines in manufacturing employment - Reduced wages for those who kept their jobs - Higher rates of long-term unemployment - Lower labor force participation - Higher rates of disability claims - Increased reliance on government transfer programs - Lower marriage rates and increased rates of "deaths of despair" (suicide, drug overdose, alcohol-related)

3. The damage was persistent. Workers displaced by Chinese import competition mostly did not move to other regions or industries. Many of them never recovered economically. The "long-run adjustment" that the simple comparative-advantage story assumes — workers reallocating from declining industries to growing ones — happened much less than expected.

4. The political consequences were measurable. Communities most exposed to Chinese import competition shifted toward more polarized political positions, with measurable effects on election outcomes. A follow-up paper by Autor, Dorn, Hanson, and Majlesi (2020) estimated that the 2016 U.S. presidential election outcome in several swing states was affected by the China shock.

What this means for the standard economic case

The China shock is not a refutation of comparative advantage. It is a refutation of the naive version of the comparative-advantage story that says "trade benefits everyone, the losers will quickly find new jobs, and the long-run aggregate gains dwarf the short-run distributional costs."

The honest version of the story includes the following corrections: - Aggregate gains exist but they're smaller than the simple story claims, because adjustment is costly, not free. - Distributional costs can be large and persistent for specific workers, communities, and industries. - The U.S. did not invest enough in helping displaced workers. Trade Adjustment Assistance (TAA), the main federal program for retraining workers displaced by trade, was woefully underfunded relative to the scale of the China shock. - The political consequences of trade liberalization are real and have shaped subsequent policy in ways the standard model didn't predict.

Most economists who work on trade today would endorse a version of this corrected story. The 2019 IGM Forum poll on the China shock showed substantial agreement among leading economists that the China shock was larger and more damaging than expected, even among economists who continue to support free trade in principle.

9.5 The political economy of trade

The China shock helps explain why free trade is so much more contested politically than the standard textbook treatment would suggest.

Why is free trade unpopular?

1. The losers are concentrated and visible. A textile worker in North Carolina who loses her job to Chinese imports knows exactly what happened to her. Her community can identify the closed factories and the lost jobs. The damage is concrete.

2. The winners are diffuse and invisible. Consumers across the country who pay slightly less for clothing don't know they're benefiting from free trade. They don't show up to political rallies thanking China for cheaper T-shirts. They don't form lobbying groups for free trade. The benefit is real but unrecognized.

3. The asymmetry creates political pressure to restrict trade. Concentrated losers organize. Diffuse winners don't. The result is that trade restrictions are politically easier to enact than to remove, even when the aggregate welfare costs are clear.

4. Trade-displaced workers do not always recover. The standard model assumes workers can move to other jobs and other industries. The empirical record shows that many do not — particularly older workers, workers in regions with weak labor markets, workers without easily transferable skills. The "long-run adjustment" assumed by the model often takes a generation or doesn't happen at all.

5. Trade interacts with other inequalities. The communities most exposed to trade competition were often already economically vulnerable. Trade made things worse, on top of pre-existing problems.

Why do economists still mostly support free trade?

Despite the China shock and its lessons, the IGM Forum poll consistently shows ~85% of leading economists agreeing that free trade is, on balance, beneficial. Why?

Several reasons: 1. The aggregate gains are real and large. Even after accounting for adjustment costs, the net welfare effect of free trade is positive in most analyses. 2. The alternative is worse. Protectionism has its own costs — higher consumer prices, less efficient industries, retaliatory tariffs from trading partners, slower productivity growth. Most analyses find that trade restrictions cost more than they save. 3. The right response to distributional damage is compensation, not protectionism. The economic case is that we should help displaced workers (through training, income support, regional assistance) rather than restrict trade. The political case is harder, because compensation programs are notoriously underfunded. 4. The China shock was unusual. The combination of WTO accession + Chinese productivity boom was a one-time event. Most trade liberalization in modern history has not produced damage on this scale.

But the economist consensus is more nuanced than the simple "free trade is good" framing of older textbooks. The honest summary: free trade increases total welfare, but the distribution matters and we have not historically done a good job of compensating losers, and the political consequences are real.

9.6 What economic analysis can and cannot tell you

The standard analysis tells you: - Free trade increases total surplus (with caveats about who captures it) - Tariffs and quotas reduce total surplus and create deadweight loss - The size of the welfare cost depends on the elasticities involved - Distributional effects can be large and concentrated

The analysis does not tell you: - How to weight the gains for many vs. the losses for few - Whether to compensate trade losers, and if so, how much - Whether some industries are strategically important enough to protect even at welfare cost - How to handle non-economic considerations (national security, environmental standards, labor rights) - What the right response is when trading partners don't reciprocate

These are the questions that animate trade policy debates. Economic analysis informs them but does not settle them.

The honest synthesis: free trade is, on net, beneficial — but the "on net" hides important distributional questions, and the historical record shows that the U.S. has not adequately addressed the distributional concerns. The right response is not to abandon free trade but to do a better job of compensating its losers. Whether this is politically possible is a different question.

Key terms recap: tariff — a tax on imports quota — a quantity restriction on imports world price — the international market-clearing price imports / exports — goods coming in / going out terms of trade — the rate at which goods are exchanged China shock — the rapid increase in Chinese imports starting in 2001 protectionism — policies that restrict imports to protect domestic industries Trade Adjustment Assistance — federal program to help workers displaced by trade

Themes touched: Markets power+imperfect, Tradeoffs, Disagreement (about how to weight the China shock damages), Affects daily life, Data tells stories (about the empirical surprise).