All this has revealed weaknesses in emerging-market economies that were camouflaged by the commodities boom. Brazil is struggling with high inflation, big budget deficits and a corruption scandal involving Petrobras, the national oil company. China is striving to “rebalance” its economy — shifting “from industry to services, from exports to domestic markets, and from investment to consumption,” as Lagarde put it. These problems are not superficial or easy to solve; they take time.

As a result, international trade and investment — engines of the world economy — are languishing. For many years, international trade grew faster than the world economy. From 1997 to 2006, trade expanded 6.8 percent annually compared with 4 percent growth for the world economy. The gap reflected greater globalization: more cross-border supply chains and more specialization. Now this is no longer true. In 2015, both trade and the world economy grew at about 3 percent.

The same thing has happened to foreign direct investment (FDI): factories and businesses in emerging-market countries owned by outsiders. In 2015, FDI in 30 emerging market countries totaled $488 billion, down from a peak of $606 billion in 2011, says the IIF.

The United States cannot isolate itself from these realities.