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, aging, emigration, for example as a result of economic recession, urban decay, rural flight, food resource decline or high death rates due to violence, disease, or other catastrophes.. Generally, population decline is perceived as a negative occurrence by policy makers, because a large population is traditionally associated with great power status; for this reason, many governments are trying to halt or reverse declining trends in population. However, depopulation in humans can be largely beneficial for a region, allocating more resources with less or no competition for the new population. In addition to exempting the disadvantages of overpopulation, such as increased traffic, pollution, real estate prices, environmental destruction, and fossil fuel usage, etc. 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, carbon neutrality and negativity, reforestation, including nitrogen fixing trees, return of native species such as salt marshes and mangroves, reduction of pollution and urban heat island effect , buying more time for people to fight the climate crisis, 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.