As i learn more about the history of Middle Earth i am surprised just how many close calls people in ME had trough history, in particular it seems like "let's keep all our eggs in one basket" is the motto of the day. I think the first instance of it is Gondolin, it is said Gondolin was the last free place in ME in it's time, there were no signifficant elven populations anywhere else, and then it fell, had Valar not gotten involved that would be it for both Elves and Men in ME. However at least Elves have a backup in Valinor, if all elves in ME got slaughtered there would still be elves in Valinor.
Dwarves however had no such luck, and considering how many times they avoided extinction by the merest of margins one would think they would learn to spread out their number a bit, so that when one of their settlements gets hit by a dragon or some other thing they don't all get slaughtered at the same time, first it was Moria, for some reason when Moria was settled all dwarves everywhere decided to abandon their home and settle there, tough luck when they awakened Durin's bane and got slaughtered.
One would think that after this close call they would learn to spread out a bit, but no, they inhabit Erebor and Grey mountains, and for some strange reason they decide to abandon Erebor and all go live in the Grey Mountains, and lo and behold, come dragons and once again dwarves are nearly exterminated, but do they learn from this?
No, they abandon Grey Mountains and once again they settle in Erebor, but once again they are all concentrated in one place and that means when Smaug comes he has a very god chance to exterminate dwarves then and there, had he not been more interested in the gold there is a good chance of no more dwarves.
And they for some reason still don't learn their lesson, they once again almost all settle in the Iron hills, granted at the end of the third age and beginning of the fourth age they spread a bit and repopulate Erebor and Blue Mountains, and Gimli leads a colony to the glittering caves, but still, four cities seem way too few for comfort.
The same problem plagues free peoples, though there are other people in ME the free peoples seem to have chronic shortage of settlements, when Arnor falls in the second age nobody thinks to repopulate the area until the end of the third age, the whole northwestern part of ME is practically deserted despite it being speciffically stated that no orc remains alive there.
Dale is the only great city in the north and it gets wrecked by Smaug, it's people find the Lake Town but they are in constant danger of being destroyed by Smaug, which nearly happens when Thorin and company awaken him, had Bard not killed Smaug in a lucky shot there is a good chance that people of the North would be reduced to a handful of villages.
Which brings me to Rohan, who are also of descendents of northmen, they had a pretty close call with Waine Riders, how Northmen and Gondor managed to regroup and strike back after being almost totally defeated is beyond me but Northmen almost died out in that battle, luckily fot ME they survived and moved to the vale of Anduin, where they somehow managed to evolve into Rohirrim, trough thousands of yearsthey ended up occupying only a small sliver of land in the north, and even that was abandoned when they went to settle Rohan, one would think some of them would stay but apparently not, they all left and moved to Rohan, right after avoiding another close call where Gondorian armies were nearly wiped out.
And lastly the Hobbits, how they even managed to survive as long as they did is beyond me, apparently there are only about 3000 of them and they only live in Shire and Bree, that is barely a stable enought populatuion to maintain genetic diversity as it is, and apparently there are no hobbits anywhere else, so if they get hit by some kind of plague or orc invasion they are done for.
It seems like ME in general is plagued by a singular problem, various races seem to go out of their way to reduce their own number and avoid setting up colonies even during long times of peace, in fact the only race that seems keen on expanding is Orcs, which explains why they always seem to outnumber all the other races by the order of magnitude, because they seem to be the only ones to think "look, empty land, lets live there"
TLDR: Races in ME excepting orcs seem to go out of their way to only live in select few places despite having a lot of free alnd available, leading to them constantly being one step away from total annihilation.
EDIT: Fixed an excessively long title. ~recneps