With worldwide population growth curves flattening and population pyramids inverting, countries of tomorrow will be positively clamouring for immigrants.

A good book to read on the topic is Empty Planet by Bricker & Ibbitson[1]. One of their observations is that the country best placed to weather the coming demographic storm is the US, as they have a ready supply of immigrants south of their border. Every other country will have to compete, and some such as China will be in dire straits due to past misguided policies.

[1] https://www.goodreads.com/book/show/37585564-empty-planet