Read Krugman's numerous works on the topic and for which he was awarded the Nobel prize last year. What he found was that most trade occurs NOT between countries with comparative advantages between each other, but between countries with almost identical factor costs in labor, capital, regulation, unionization, etc.  Most trade occurs between countries that are almost entirely alike.  US-Canada. EU-EU. Japan - US.  Etc.  Krugman asked how this could be true if the neo-classical trade theories of Storper-Samuelson (which models trade as returns to labor and capital in different countries) or Heckscher-Ohlin (a more advanced version of the classic Ricardo model of abundant and scarce factors) were also true, and he finds that they can't -- that another explanation of trade was required to explain the most common type of trade in the late 20th century-- intra-firm transfers.