[Rumil]

Aha, wild speculation called for!

As Tolkien really didn't give us any firm information on population sizes, I think its up to us to discuss the subject. I've got a useful little book which includes information on populations in Dark Age and Medieval Europe, so will dig this out and see if I can post some useful figures.

In the meantime though, as has been said, the population of Britain was about 3 million after the Black Death etc. However, during the 'darkest' bits of the Dark Ages, around 700AD, it's estimated to have been nearer 1 million.

Explanations for population decline are various, including plagues, warfare, climate change, crop faliures, even asteroid strikes!

I think the Middle Earth situation ties in with a belief that when the rightful king is absent from a country, its fertility declines, both in terms of crops and people. This probably goes way back, I remember hearing that in Ancient Egypt the pharaohs had to carry out some very peculiar rituals in order to ensure that the Nile kept on flooding every year to irrigate the crops. Likewise in one of the King Arthur films (with lots of irritating plate armoured knights as I remember), when the King returns, the land blooms and spring comes again. I'd imagine this sort of belief arose because during times of weak kingship there is often endemic civil war (see Stephen and Matilda). As well as battle casualties there would likely be bad harvests because men were forced to fight rather than tend their fields.

In Gondor of course, there may be more specific mechanisms to consider. Sauron had unleashed great plagues on the West previously in the third age. I'd bet that his 'broils and smokes' emanating from Mount Doom were spiked with endocrine disrupters (chemicals which may reduce fertility).