We propose a unified model of growth and internal migration and identify its deep parameters using an original set of Swedish data. We show that internal migration conditions had to be favorable enough to induce an exodus out of the countryside in order to fuel the industrial development of cities and the demographic transition of the country. We then compare the respective effects of shocks to internal migration costs, to infant mortality and to the productivity of rural industry to the economic take-off and demographic transition that occurred in Sweden. Negative shocks to internal mobility generate larger delays in the take-off of growth than do mortality shocks equivalent to the bubonic plague. These delays are dramatic when rural industry is less productive in the early phase of industrialization. The economic and demographic dynamics of Sweden were very similar to those of the rest of Europe at the time of industrialization, which allows us to generalize our findings.