In the decades leading up to the 2008 financial crisis, international trade typically grew much faster than GDP.
This reflected increasing global economic integration: tariff barriers were coming down, trade groups (eg. the eurozone, NAFTA, ASEAN) facilitated trade through regulatory simplification, costs of international transport fell with containerisation and bulk shipping, and the supply-chain revolution spread production between countries.
But since 2008, international trade hasn't (quite) kept pace with GDP growth.
It doesn't seem to be just the disruption of 2008 and the slow recovery, as growth during this period was much the same as in the two decades before 2000. Maybe the fast growth of trade reflected a series of one-off institutional changes and trade agreements: the formation of the European Community, NAFTA and China joining the WTO in 2001. [fold]
Perhaps it's unrealistic to expect trade to go on growing appreciably faster than GDP forever. When Thomas Friedman's 'flat world' arrives, or the Japanese 'flying geese' finish taking most manufacturing production to cheap-labour economies, there will no longer be a reason for trade to grow faster than GDP.
Whatever the reason, the slow growth of trade is unhelpful for the global recovery. There is still the chance that America's 'platinum standard' trade deals, like the TPP and TTIP, will come to pass and provide big boosts to global trade.
But one other indicator suggests that the momentum of global economic integration is running out of puff. Foreign direct investment has grown more slowly recently than earlier in the century.
Again, it may be that the 'low-hanging fruit' was picked in the early decades of integration, but the benefits of integration are far from over.