What factors does Paul Krugman identify that supported expanding international trade in the 1800s?

Is the exchange of capital goods and services across international borders or territories because there is a need or want of goods or services. In most countries, such trade represents a significant share of gross domestic product. This theory of international trade is further supported by Paul Krugman.

Basically, Paul Krugman mentions 1869 as the year in which both the Suez Canal and the Union Pacific railroad were completed and hence facilitated the expansion of trade. Further stream ships and railroads had created markets for standardized commodities for a better global reach. Moreover, the global flow of information was better with improved electronic technology, submarine telegraph which helped economic regions to communicate effectively.