A population decline (or depopulation) in humans is a reduction in a human population caused by events such as long-term demographic trends, as in sub-replacement fertility, urban decay, white flight, or rural flight, or due to violence, disease, or other catastrophes. Contrary to contemporary belief, depopulation can be largely beneficial for a region, allocating more resources and less competition for the new population, in addition to exempting the disadvantages of overpopulation, such as increased traffic, pollution, real estate prices, and environmental destruction. Per-capita wealth may increase in depopulation scenarios, in addition to improvement of environmental quality-of-life indicators such as improved air and water quality, reforestation, return of native species, etc. The accompanying benefits of depopulation have been termed shrink and prosper, with benefits being similar to the post-Civil War Gilded Age, post-World War I economic boom, and the post-World War II economic boom.
Many countries in Europe are faced with a huge net decrease in population and hence an increase in the average age of the working population. Some countries face the first large population reduction since the Black Death plague in the 14th century.