Migration, trade, and development: an overview

Simple, neoclassical economic models predict that prices should drive factors such as labor and capital across regions and countries toward their most valuable use. As this happens, developing countries, which are typically labor-rich and capital-scarce, should experience more rapid growth, higher income, and eventually convergence to industrial world levels of well-being. This process is happening slowly in some cases, but in other cases not at all. Do migration and trade speed this convergence? If so, how? If not, why?