 How does the proportionality principle work? The idea is that potential migrants can be excluded from states or areas of the world where people are over-using (or using at the average level) the resources, but they cannot be excluded from the areas where the resources are ‘under-used’. This brings in a rather technical discussion of what constitutes ‘over-use’ and ‘under-use’, but the most consistent formulation is that one is ‘underusing’ a territory when the ratio of a state’s population to the value of its natural resources is low compared to the other states, and ‘over-using’ it when the ration is high (see Blake &amp; Risse 2008; Risse 2012: 158–166).