人口不足
Population decline can cause internal population pressures that then lead to secondary effects such as ethnic conflict, forced refugee flows, and hyper-nationalism. This is particularly true in regions where different ethnic or racial groups have different growth rates. An example of this is white nationalism. White nationalists seek to ensure the survival of the white race, and the cultures of historically white nations. Many white nationalists believe that white people should therefore maintain a demographic majority and that mass immigration of non-whites and low birth rates among whites are threatening the white race. Low fertility rates that cause long-term population decline can also lead to population ageing, an imbalance in the population age structure. Population ageing in Europe due to low fertility rates has given rise to concerns about its impact on social cohesion.