Final answer:
The correct option is b. Paul Krugman attributes technological advancements and globalization as factors for international trade expansion in the 1800s, underpinned by the principle of comparative advantage and later supported by international trade agreements like GATT.
Step-by-step explanation:
Economist Paul Krugman identifies technological advancements and globalization as key factors that supported the expansion of international trade in the 1800s. These developments led to reductions in transport costs and improved communication, which facilitated the exchange of goods across national borders. Additionally, the economic theory of comparative advantage became widely understood during this time, prompting nations to specialize in the production of goods where they held a productivity edge and to trade for other products, thereby gaining from such trade.
The creation of international trade agreements, such as the General Agreement on Tariffs and Trade (GATT), further expanded trade by providing a framework for countries to negotiate tariff reductions and address other trade barriers. This cooperation among nations, although focused on reducing protectionism, acknowledged the domestic costs that could arise from trade barriers and sought to create a system that would maximize the economic benefits of international trade.