Chapter 2
World Trade: An Overview
◼ Chapter Organization
Who Trades with Whom?
Size Matters: The Gravity Model
Using the Gravity Model: Looking for Anomalies
Impediments to Trade: Distance, Barriers, and Borders
The Changing Pattern of World Trade
Has the World Gotten Smaller?
What Do We Trade?
Service Offshoring
Do Old Rules Still Apply?
Summary
◼ Chapter Overview
Before entering into a series of theoretical models that explain why countries trade across borders and the
benefits of this trade (Chapters 3–11), Chapter 2 considers the pattern of world trade that we observe today.
The core idea of the chapter is the empirical model known as the gravity model. The gravity model is based
on the observations that (1) countries tend to trade with nearby economies and (2) trade is proportional to
country size. The model is called the gravity model, as it is similar in form to the physics equation that
describes the pull of one body on another as proportional to their size and distance.
The basic form of the gravity equation is Tij = A Yi Yj/Dij. The logic supporting this equation is that large
countries have large incomes to spend on imports and produce a large quantity of goods to sell as exports.
This means that the larger that either trade partner is, the larger the volume of trade between them. At the
same time, the distance between two trade partners can substitute for the transport costs that they face as
well as proxy for more intangible aspects of a trading relationship such as the ease of contact for firms. This
model can be used to estimate the predicted trade between two countries and look for anomalies in trade
patterns. The text shows an example where the gravity model can be used to demonstrate the importance
of national borders in determining trade flows. According to many estimates, the border between the
United States and Canada has the impact on trade equivalent to roughly 1,500–2,500 miles of distance.
Other factors such as tariffs, trade agreements, and common language can all affect trade and can be
incorporated into the gravity model.
4 Krugman/Obstfeld/Melitz • International Economics: Theory & Policy, Tenth Edition
The chapter also considers the way trade has evolved over time. Although people often feel that
globalization in the modern era is unprecedented, in fact, we are in the midst of the second great wave of
globalization. From the end of the 19th century to World War I, the economies of different countries were
quite connected, with trade as a share of GDP higher in 1910 than in 1960. Only recently have trade levels
surpassed pre–World War I trade. The nature of trade has changed, though. The majority of trade is in
manufactured goods with agriculture and mineral products making up less than 20 percent of world trade.
Even developing countries now primarily export manufactures. A century ago, more trade was in primary
products as nations tended to trade for things that literally could not be grown or found at home. Today,
the motivations for trade are varied, and the products we trade are increasingly diverse. Despite increased
complexity in modern international trade, the fundamental principles explaining trade at the dawn of the
global era still apply today. The chapter concludes by focusing on one particular expansion of what is
“tradable”—the increase in services trade. Modern information technology has expanded greatly what can
be traded as the person staffing a call center, doing your accounting, or reading your X-ray can literally be
halfway around the world. Although service outsourcing is still relatively rare, the potential for a large
increase in service outsourcing is an important part of how trade will evolve in the coming decades. The
next few chapters will explain the theory of why nations trade.
◼ Answers to Textbook Problems
1. There are a number of reasons for this difference. Canada’s trading patterns are largely explained by
2. According to the trade gravity equation model, trade exchanges are positively affected by size of
trading economies and negatively affected by their distance. Other conditions being the same, two
3. No, if every country’s GDP were to double, world trade would not quadruple. Consider a simple
example with only two countries: A and B. Let country A have a GDP of $6 trillion and B have a
GDP of $4 trillion. Furthermore, the share of world spending on each country’s production is
proportional to each country’s share of world GDP (stated differently, the exponents on GDP in
Equation 2-2, a and b, are both equal to 1). Thus, our example is characterized by the table below:
Country
GDP
Share of World Spending
A
$6 trillion
60%
B
$4 trillion
40%
Now let’s compute world trade flows in this example. Country A has an income of $6 trillion and spends
40 percent of that income on country B’s production. Thus, exports from country B to country A are
Chapter 2 World Trade: An Overview 5
What happens if we double GDP in both countries? Now GDP in country A is $12 trillion, and GDP in
country B is $8 trillion. However, the share of world income (and spending) in each country has not
changed. Thus, country A will still spend 40 percent of its income on country B products, and country
4. As the share of world GDP that belongs to East Asian economies grows, then in every trade
relationship that involves an East Asian economy, the size of the East Asian economy has grown.
This makes the trade relationships with East Asian countries larger over time. The logic is similar to
why the countries trade more with one another. Previously, they were quite small economies,
meaning that their markets were too small to import a substantial amount. As they became more
wealthy and the consumption demands of their populace rose, they were each able to import more.
5. As the chapter discusses, a century ago much of world trade was in commodities, which were in
many ways climate or geography determined. Thus, the United Kingdom imported goods that it could
not make itself. This meant importing things like cotton or rubber from countries in the Western
Hemisphere or Asia. As the United Kingdom’s climate and natural resource endowments were fairly