“It is an accepted maxim of international law that every sovereign nation has the power, as inherent in sovereignty, and essential to self-preservation, to forbid the entrance of foreigners within its dominions ...”

An accepted maxim of law? —  Not a law itself,  hmmm. Obviously couching the concept in the philosophy of legal positivism. If the "maxim" is of international law; what is stated by national law. An overview probably rates 5 stars.

Good point, Mike.  It would be better if that power was not assumed...