A close look at this situation shows that many of these overpopulated nations mostly in Africa and Asia are underdeveloped. While these underpopulated nations are economically buoyant. I think the reason for the poverty of these developing nations is not the population but bad governance and the inability to maximize and distribute available resources equally. We cannot deny the fact that these overpopulated nations are economically important to these developed nations in terms of human resources. And they contribute immensely to the development of these first-world nations in terms of cheap labour.
I can say under-development, late development, economic struggle, poverty, and anything like that wasn't caused by over population. It's more of a bad governance. I mean pretty bad governance. Corruption is the leading reason for this. The huge number of population the more progressing the country should be, but it turns out to be the other way around. That's what happens when politics becomes a business rather than it's true purpose "public service".
Big business men paying these political leaders straight to their pocket to prevent more investors/business competitors from entering the city, thus preventing employment opportunities as well. That's where massive unemployment was created.