In 1950 North Americans and Europeans were more than 28% of the world’s population. A century later this will be 12%.
In 1950 Europe had more than twice as many people as Africa. A century later Africa will have three times as many people as Europe.
The median age of people in Western countries is much older than in developing countries.
For demographic reasons alone there will be a shortage of qualified labour in Western countries.
Demographic change will make it difficult to recruit armies from a diminishing pool of young adults. [There is also a large chemical-induced decline in the birthrate and fertility of males worldwide.]
As populations age and the proportion who are native (born in the country) declines it is inevitable that the ethnic cultural and religious backgrounds of the country will quite literally change as immigrants from vastly different cultural and religious backgrounds grow in numbers.