From the abstract:
The libertarian first principle—a belief in individual freedom—can lead to two different and not necessarily acceptable societies from the standpoint of liberty. One is the “Union of Liberty,” in which communities, associations, and intermediate bodies are held to rigorous standards of voluntariness (and thus face sharp limits on their internal associational freedom because of the knowledge that children will be born into them). In the other, the “Federation of Liberty,” they are not (thereby allowing children to be born into locally unfree environments).
The whole thing's just 13 pages long, and well worth a read.
[via the IEA blog]