Reasons for Norwegian emigration. 1880-->

This website: http://www.digitalhistory.uh.edu/historyonline/italian_immigration.cfm provides some interesting key points as to why Italians emigrated to the US at the end of the 19th century. (Overpopulation, lack of fertile soil, high taxes, natural disasters, etc) I'm writing an essay on remigration ("tilbakevandring") and I'm using Italy and Norway as examples. What were the reasons for Norwegian emigration to the U.S at towards the end of the 1800s? According to Mark Wyman's "Round trip to America - The immigrant's return to Europe "1880-1930" it has to do with a general lack of land due to some sort of heritage law granting only 1 child the family farm while rendering the siblings homeless. Are there any other, more detailed reasons?