Every species, including humans, are generally always suffering the effects of overbreeding. When a species is suffering the effects of overbreeding, births cause the death of children. Every species breeds faster than required to maintain their numbers. The ones that did not, have gone extinct. All have a finite environment, and sufficient time, thus all species are at the limit of what the environment can provide. This includes humans too. There are exceptions, but they are only temporary.
When a species invades a new territory, or some disease wipes out large numbers, the survivors will be below the limit and while their numbers grow back to the limit they are not suffering the effects of overbreeding. Humans are unique in that we have the ability to discover and use better technologies to increase the capacity of our environment.
We have a world economy which means that there is only one environment, the whole Earth. Inexpensive shipping allows the inhabitants of what seems like a separate environment to use the production of another environment. The fact that you can eat a coconut in Seattle and that people live on Antarctica shows this. The average number of children for the whole population is too high which creates the horrible high child mortality found in developing countries. In addition, our ignorance of the fact that averaging too many babies causes the death of children, results in the associated dreadfully low adult life expectancy in those same countries.
A birth anywhere, to rich or poor, contributes to the death of a child somewhere.