"By virtue of events that have already transpired and public policies already in place, the 1990s will witness the largest inflow of immigrants into the population and labor force of the US of any decade inn the nation's history. The revival of the phenomenon of mass immigration from out of the nation's past began in 1965. Unlike earlier mass immigration periods to the US, the post-1965 wave of immigrants shows no sign of imminent decline. For a variety of reasons, immigration is a subject that is especially amenable to study and interpretation by institutional economists. In today's world setting, international migration is a discretionary action that is regulated by the specific actions of the governments of individual nation-states. To the degree mass immigration takes place, it is a policy-driven phenomenon. There is no international obligation for any nation to allow others to enter or to work or to permanently settle within its geographical borders. In fact, most nations do not admit immigrants for permanent settlement."