For a lot of western Europe the colonies were used as dumping grounds. Some of it was to dispose of convicts, but there were also trends in agricultural mechanization even while still powered by horse and steam. That created a large population of rural serfs no longer needed or desired.
By the 19th Century some countries got "scientifically" precise about this. Eugenics was in vogue long before the 1930s. It is no accident that the Netherlands saw such a radical shift toward its population's stereotypical characteristics today. Partly through selection, partly through redistributing available resources including education, housing, nutrition, and sanitation. Most of that accomplished by Church and State working hand in hand to dispose of the "excess population."

