For the United States, foreign trade in goods represents scarcely a fourth of GDP today. The openness of today’s 27-member European Union is of about the same order of magnitude. However, this similarity conceals significant differences in trend.
The United States built its internal market much earlier than Europe, in the nineteenth century; and even in the 1950s and 1960s American foreign trade was much more modest than now, accounting for just one tenth of GDP. The dynamics was very different. The US were a closed economy with a predominant internal market until recently.