Across much of Europe in the late nineteenth century there was a fundamental problem, notably in those zones where industrialisation had had little impact and where the agricultural sector confronted declining returns to labour. Population growth was evidently occurring in a transforming context of agrarian and industrial change, which carried the ultimate causes of mass migration. The absorbent capacity of European cities and towns was the critical factor in the long run. The scale of intra-European migration was extraordinary: Europe's industrial cities attracted foreigners in vast numbers. The Canadian historian Norman Macdonald declared that the great diasporic European phenomenon was a migration with 'many roots, chiefly the adverse conditions in the Old World and the appeal of the New'. By the late nineteenth century, emigrants were streaming out of most parts of Europe.