I agree with everything Wendy said except for her 5th point.
Human birth rates are declining and populations will start declining around 2050.
Human birth rates have been declining since circa 1970. Once young women get enough education that they can earn dollars outside of the house, they also realize that modern medicine has reduced infant mortality rates to the point that most of their children will survive to adulthood. Ergo little need to birth more than 2 or 3 children.
First World birth rates have been below replacement rates (2.2 children per woman) for even longer. Second World birth rates have also been declining to below replacement rates. It is only a few Third World countries that still have high birth rates. See Nigeria which is the most populous country in Africa and projected to exceed the population of main land China by 2050. How Nigeria can feed that many mouths with a swampy Southern coast-line and an arid northern third is a mystery to me???????
Low birth rates force First World countries to accept thousands of immigrants per year to do lower-paying jobs. For example, British Columbia has to import hundreds of seasonal Mexican farm laborers (fruit-pickers) every summer because Canadian citizens do not want to work long days for minimum wage.
Several first world countries are already experiencing serious labor shortages because of low birth rates. Main land China's "One Child Policy" may have solved a population problem, but it created other problems. Gender-specific abortions reduced the number of baby girls to the point that main land China now suffers from a shortage of brides ... conversely ... an excess of un-married young men. Un-married young men are far more likely to riot, etc.
OTOH low birth rates can drive global politics in unpleasant ways. Consider the current Russian problem of too few young men of military age. If you look back a century, a Russian boy born in 1920 had only a 20 percent chance of surviving World War 2 (ended in 1945). Many millions of those deaths were during battle, but huge numbers also died during the Russian Revolution, Ukrainian Civil War,, Stalin's Purges, Holomodor Famine, occupation of Afghanistan during the 1980s, Chechin Wars, etc. Russia also suffered low birth rates during the confusing period after the Iron Curtain fell. Current Russian birth rates are hampered by age, alcoholism and abortions. Age problems are the results of a series of waves of birth rate slumps echoing back to the 1930s. With shortages of young men of marriageable age, few young Russian women want to raise families as single mothers. Alcoholism is caused by all the cheap vodka causing "brewer's droop" and shortening the lives of Russian men since Tzarist times. Finally, abortion is the only form of pre-natal care available to to millions of Russian women.
Mr. Poutine felt compelled to invade Ukraine this year, because he knew that if he waited another decade, he would not be able to field enough soldiers.
Russia is reluctant to admit immigrants who are visible minorities. This xenophobia is understandable given all the times that Russia has been invaded by: Austrians, British, French, Germans, Hungarians, Kyrgyrs, Lithuanians, Ottomans, Poles, Swedes, Sythians, Turks, Vikings, etc. Moscow suffers from too few natural lines of defense across the North European Plain. THE NEP extends from the Normandy Coast all the way to the Ural Mountains.
I want to make it clear that I understand the paranoia that drives Mr. Poutine's current invasion of Ukraine, but Mr. Poutine's paranoid does not justify the current slaughter in Ukraine.