I think by "single division of labor" he means that there's one global labor supply which gets stratisfied across countries, "trans-national" labor supply. So s

I think by "single division of labor" he means that there's one global labor supply which gets stratisfied across countries, "trans-national" labor supply. So some countries have most of their workers performing so-called "high-skill" capital-intensive production (first-world "core" countries, eg Hershey's imports cocoa, then processes it in the US to produce chocolate). Other countries develop a more blue-collar labor-intensive job supply, for the extraction of raw materials (cocao farmers in the Ivory Coast producing raw exports). "Multiple divisions of labor" would mean that each nation maintains its own, sovereign hierarchy of labor. It describes economies prior to globalization, when nation-states tended to do most of their trade internally, rather than across huge geographic distances and political lines.