Internationalism is a social and political theory, a certain concept of how human society ought to be organized, and in particular a concept of how the nations ought to organize their mutual relations.

His daughter Thora was a history and language teacher from 1938 at Oslo Cathedral School. During the occupation of Norway by Nazi Germany Christian Lous Lange joined the resistance movement while her husband went in exile. He was one of the world's foremost exponents of the theory and practice of internationalism.

He was the father of Carl Viggo Manthey Lange Halvard Lange and Christian August Manthey Lange. Lange died at the age of 69 one day after the 17th anniversary of his receipt of the Nobel Prize.