The following are the largest population concentrations in the world, each with over 100 million people. These concentrations are a mix of countries and provinces; I allow this because some of the provinces, due to populations, have nearly the same impact as countries. I do not include China (1.3 billion) and India (1.2 billion) on the list because "huge population" subsets are already there. As such this is a little bit of an arbitrary list, but I think it has value. Together these concentrations represent nearly 2 out of 7 people on our planet. I list them here because, although they each contain within themselves numerous people groups and sociopolitical subsets, each of them also represents something of a "hard boundary" between other population concentrations. Each has characteristic geographic, political, economic and religious situations where the subsets they contain have more in common with each other than with others outside. Strategies that seek closure will have to be able to scale to reach the geo/political/ethno/linguistic boundaries of these concentrations. (The concentrations are a mix of countries and provinces; I allow this because some of the provinces, due to populations, have nearly the same impact as some countries!)
It would behoove every mission agency, church, denomination, and student of mission history to at least be familiar with these 13 populations and reflect on how their strategies impact them. There are enormous disparities of ministry resources between these, and strategists and students could reflect on (a) the imbalances, (b) the obstacles, (c) what can be done to redress these. If any single one of these populations were dramatically changed, it would transform the region they are in and the world in general.