The following is from Bertrand Russell's Political Ideals
When any group of men has a strong corporate consciousness--such as belongs, for example, to a nation or a trade or a religious body--liberty demands that it should be free to decide for itself all matters which are of great importance to the outside world. This is the basis of the universal claim for national independence.
(emphasis by me)
What does the author mean by "the outside world"? Does it mean the real world as opposed to the mental world? Does it mean the other groups?