Where have all the dragons gone?

Question

Related to the question: How could Thranduil have met a dragon?

It seems that there was a time in Tolkien's legendarium when dragons roamed the land and were a real and physical force to be reckoned with, and not just distant memories of terror. But in the events of LOTR and The Hobbit, we only know of Smaug, a Fire Drake and the flying mounts of the Nazgûl — and they, as a friend would put it, are to dragons what puppies are to wolves.

Whatever happened to the dragons? Why haven't we heard of them in the times closer to the events of the Third Age?

Answer 1

There aren't a lot of mentions about what happened to dragons, but here is what I could find:

Dragons were created by Morgoth. Many of them died at the War of Wrath (at the end of the First Age. That is why there aren't a lot of dragons in the Thirds Age)

(J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion):

During the War of Wrath, Morgoth unleashed a new terror upon Middle-earth -- the winged dragons. Chief among these was Ancalagon the Black. Eventually slain by Eärendil the Mariner, Ancalagon's fall crushed the towers of Thangorodrim. Many of the dragons were destroyed in the War of Wrath but some fled and survived into the later Ages.

The greatest and most fearsome (mentioned) dragon that lived in the Third Age was Smaug.

Gandalf told Frodo:

(J.R.R. Tolkien, The Lord of the Rings, The Fellowship of the Ring, "The Shadow of the Past")

[...] there is not now any dragon left on earth in which the old fire is hot enough [to melt the Rings of Power]

indicating the presence of other, lesser dragons.

(J.R.R. Tolkien; Humphrey Carpenter, Christopher Tolkien (eds.), The Letters of J.R.R. Tolkien, Letter 144, (dated 25 April 1954))

What we know from the Lord of the Rings' Appendices is that after the First Age, the Dragons appeared to move north to Northern Waste.

It would appear that the dragons fled to the Northern Waste, far from the lands of Men and Elves. Over the centuries, the race of dragons continued to breed and repopulate, particularly in the Withered Heath, an area in between two spurs of the Grey Mountains.

(J.R.R. Tolkien, The Lord of the Rings, Appendix B, "The Third Age" , Appendix A, "Durin's Folk"):

In the late Third Age the dragons of the Withered Heath, stirred by the return of Evil, began to harass the Northmen and make war with the Dwarves around the year T.A. 2570 (Dáin I and Frór of Durin's folk were killed by a great cold-drake in 2589). It was perhaps in these wars that dragons swallowed four of the Seven Dwarf-rings.

Here is what we know about Smaug (from the Hobbit):

The most fearsome dragon of the Third Age was Smaug, who laid waste to the Dwarf-realm of Erebor and the nearby town of Dale. This devastated the area and sent Durin's folk into exile. Smaug remained in the abandoned halls of the Lonely Mountain for many years until the coming of Thorin and Company and their "burglar", the hobbit Bilbo Baggins. This began a chain of events that led to Smaug's death at the hands of Bard the Bowman.

Answer 2

I believe that "The Akallabeth" in The Silmarillion mentions dragons among the dangers of Middle-Earth about Second Age 500, leaving Sauron to conclude that Eru and the Valar had forsaken Middle-Earth.

Dragons were amoung the evil things which began to stir again in the Third age.

The Dwarves hid themselves in deep places, guarding their ancient hoards; but when evil began to sir again and dragons reappeared, one by one their ancient treasures were plundered, and they became a wandering people. Moria for long remained secure,...

The Return of the King Appendix B, the Tale of the Years, introduction to the Third Age.

So the first dragon attacks on Dwarf realms would have begun about 1050, when the Shadow fell on Greenwood the Great, or about 1300, when evil things began to stir again. I suspect that Moria in 1980-81 was the last of the seven Dwarf kingdoms to fall.

In Third Age 1977 Frungor or Frumgar led the Eothed north to the headwaters of the Anduin.

The Return of the King Appendix B, the Tale of the Years.

Of his son, Fram, they say that he slew Scatha, the great dragon of Ered Mithrin, and the land had peace from the long-worms afterwards.

Return of the King Appendix A, II The House of Eorl

A group of Dwarves claimed the hoard of Scatha, which may have been stolen from their ancestors.

Thus Scatha may have destroyed an ancient city and kingdom of one of the seven races of the Dwarves somewhere in Ered Mithrin The Grey Mountains.

I suspect that Fram killed Scatha decades before 2077, and that by then six of the seven ancient kingdoms of the Dwarves in Middle-earth had been destroyed by dragons and four of the seven Dwarf Rings had been consumed by dragon fire.

In Third Age 2570 it is said:

About this time dragons reappear in the far North and begin to afflict the Dwarves.

The Return of the King Appendix B, the Tale of the Years.

In 2589:

Dain I slain by a dragon

And in 2590:

Thror returns to Erebor. Gror his brother goes to the Iron Hills.

The Return of the King Appendix B, the Tale of the Years.

Year 2770"

Smaug The dragon descends on Erebor. Dale destroyed. Thror escapes with Thrain II and Thorin II.

The Return of the King Appendix B, the Tale of the Years.

So there was a wave of Dragon attacks in the Grey Mountains from about Third age 2570 to 2770, which seems to have subsided for lack of targets soon after, since by The Hobbit in 2941 Dragon attacks were a thing of the past.

And there was an earlier wave of Dragon attacks in the Grey Mountains (and beyond?) that ended by about 2077 or probably decades earlier when Scatha was slain. This wave of Dragon attacks might have begun about 1800. An earlier wave of Dragon attacks might have been from about 1100 to about 1300, though that is speculation.

And six out of seven of the ancient kingdoms of the Dwarves were probably destroyed in the one or two earlier waves of Dragon attacks BEFORE Third Age 2570.

And there were also dragon problems in the Second Age.

There was no peace from dragons lasting all 6,011 years from the War of Wrath and the Great Battle to Third age 2570. 2