Additionally, if there weren't, in fact, substantially more Italians than say, Poles or Germans, why, then, is the image of the stereotypical Italian family in New York so ubiquitous?
The energy increases from crops gained through the Colombian exchange and lessening of early death from improved healthcare combined by the 1800's to lead to over population in Europe. 1848 became the year of revolutions. Political instability limited food supplies and limited food supplies caused instability. According to modern scholars the height of the average Italian was reduced by several inches between the 1500's and mid 1800's. The over population moved to wherever they had prospect of a better life. Europe didn't have a food surplus again until the 1950's. The Italian immigration coincided with industrialization so they ended up more in urban concentrations. Germans were earlier and came during agrarian expansion.