The source of comparative advantage, according to the Heckscher-Ohlin model of international trade, is each country’s:

In the Heckscher-Ohlin model, the source of comparative advantage is the relative amounts of labor and capital that are available in each country. Countries with more capital available relative to labor available will have a comparative advantage in producing capital-intensive goods, while countries with more labor available relative to capital will have a comparative advantage in labor-intensive goods