I believe it is countries with little money. Ethnicity doesn’t necessarily play a part in it, that’d only make sense due to geographical planning. Although countries with large geographical areas sounds probable, not every space is habitual- look at Antartica, for example. Countries with little money likely won’t be able to provide education on safe sex, leading to more accidental conceptions. Additionally, families will also likely struggle financially in order to pay for conception. For the lack of education and materials available, poor countries typically have higher population growth.