text: Obviously, there is a minimum population beyond which there are simply not enough people to make up a functioning country.  Beyond that, there needs to be enough people to have a fully functional economy.  That is, the major professions and trades must be adequately represented, as well as entrepreneurs and investors, support staff and other service workers, etc.  \n\nOnce there are enough to run the country, you start to see the disadvantages of too much population:  pressure on natural resources and infrastructure, housing and job scarcity, crowding causing delays in transportation, retail trade, etc.  Overpopulation also means a higher percentage of non-productive consumers than the system can most efficiently accommodate.  This causes pressure to create bureaucracy to control the excess population, including the increased crime rate caused by crowding.\n\nI do not know of any studies of what the optimum population is for a given type of geography under a given level of developments, etc., but most of the "civilized" world is overcrowded rather than too sparsely populated.  The only exceptions, like Canada, tend to be those in rather extremes of physical conditions.\n\nEnough to get you started?