Earlier quoted context omitted.
I don't think you're discussing in good faith there. Obviously what happens in Chad, Nigeria, and so on has relatively little consequence on what happens in America and the Western world in general.
Please don’t confuse disagreement with discussion in bad faith. I promise you I’m making a serious argument. It has consequence because trade exists. The Western world imports and exports goods to Africa. If the West loses population it doesn’t mean it loses economic output because there are customers and vendors in other countries with higher growth rates. Country boundaries are arbitrary.
And with falling fertility rates within a country you end up with heavily skewed age ratios meaning not only do you have far less people but far less of them are of working age so you get hit with a double whammy there. The age ratios similarly also strongly influence the shape of the economy which will shift to adapt to to the new demographics.