The most important social problem facing humanity at the beginning of the 21st century is the yawning divide in standards of living between the rich nations of the global North and the poor nations of the global South. The following table gives some indicia of the current gap in living standards. It shows that the majority of the population in most developing countries lives on less than two dollars a day; that in some developing countries, over a quarter of children aged 10-14 are employed in the work force; that mortality for children under five in developing countries can be ten to fifteen times as high as in developed countries; that over half the population in many developing countries lacks access to safe drinking water or sanitation; and that illiteracy rates among 15-24 year olds can be as high as 40% for males and 60% for females.
Avi-Yonah, Reuven S. "Bridging the North/South Divide: International Redistribution and Tax Competition." Mich. J. Int'l L. 26, no. 1 (2004): 371-87.