Final answer:
Nations impose population controls to manage resources and foster sustainable development. China's controversial one-child policy was an attempt to curb population growth, while other countries seek to increase their populations to stimulate economic growth and address aging workforces.
Step-by-step explanation:
Nations impose population controls to manage their resources and ensure sustainable development. For instance, China's one-child policy, which is now relaxed, influenced population growth by imposing fines on urban couples having more than one child. This policy and others aimed at population control are controversial and raise concerns regarding effectiveness, ethical implications, and social impacts.
On one hand, countries like Japan, Spain, Russia, and Iran attempt to increase population to combat an aging workforce and stimulate economic growth. However, the global challenge remains: balancing population size with the resources available, as predicted by Thomas Malthus, stating that unchecked population growth could lead to resource scarcity.
Ultimately, the goal of these policies is to avoid potential crises where increasing populations compete for finite resources, potentially leading to food shortages, conflict, and environmental degradation. The United Nations predicts a wide range of potential future global populations, but it's uncertain if growth will moderate to prevent potential crises such as those described by Dr. Ehrlich.