According to "The Last Outpost" in the first season of TNG 600,000 years ago the Tkon Empire had a population of trillions and could move stars. The empire ended when the central star became a supernova. That would have destroyed all the planets orbiting the central star. Radiation from the supernova would eventually reach neighboring star systems and might wipe out all life on their planets too.
People living in outer solar systems of the empire would have been unharmed by the supernova. But apparently the Tkon Empire was very highly centralized and the outer planets collapsed into barbarism and lost space flight capabilities.
According to "Contagion" in the second season of TNG the ancient Iconians presumably discovered warp drive and used it for centuries and millennia before developing their superior gateway technology to travel instantly between worlds, even across the galaxy. The enemies of the Iconians destroyed their home world Iconia with an orbital bombardment 200,000 years ago.
Thus the Iconians presumably had warp drive before developing a superior technology and abandoning warp drive. Then Iconia was bombarded and the Iconians either became extinct, and thus totally without warp drive, or escaped and lost all memory of both warp drive and gateway technology and all memory of their history on Iconia.
The episode "Booby Trap" in the third season of TNG mentioned the ancient war between the Menthars and the Promelians during Earth's 14th century. Both species had warp drive until the war, which seems to have been one of extermination. Apparently the last members of both species exterminated each other in the final battle at Orelious IX.
So the Menthars and the Promelians both had warp drive until they were extinct, and then they really, really did not have warp drive any more.
IN the episode "Ensign Ro" in the fifth season of TNG the Bajorans are introduced.
When Picard visits a Bajoran resettlement camp his log says:
Captain's log, supplemental. I read about the achievements of the ancient Bajoran civilisation in my fifth grade reader. They were architects and artists, builders and philosophers when humans were not yet standing erect. Now I see how history has rewarded them.
The ancient Bajoran civilization must have been very ancient.
As far as I know all members of the genus Homo walked erect, including Homo sapiens (c. 200,000 years ago to present), Homo rhodesiensis (300,000 to 120,000 years ago), Homo heidelbergensis (600,000 to 300,000 years ago), Homo ergaster (1,800,000 to 1,300,000 years ago), Homo erectus (1,900,000 to 70,000 years ago), and Homo habilis (2,100,000 to 1,500,000 years ago).
According to this article, many earlier species were partially bipedal, but Homo erectus 1,890,000 years ago was the first full time bipedal human ancestor.
So depending on how broad or narrow one's definition of "humans" is, Bajorans could have been civilized 200,000 to 1,800,000 years ago at the latest and possibly many thousands or millions of years before that.
But the present Bajoran civilization is much younger, going back at most tens of thousands of years.
In the episode "Rapture" in the fifth season of DS9, a 20,000-year-old painting is the only proof that the legendary lost city of B'hala ever existed. Oral stories and legends about B'hala may have been written down centuries or millennia later, but there are no surviving records contemporary with the occupation of the city except for the painting.
This strongly suggests that the era of B'hala was more or less the equivalent of ancient Sumeria or Old Kingdom Egypt in the history of the current Bajoran Civilization. The present Bajoran religion involves worshipping the Prophets who sent the Orbs to Bajor over the last last 10,000 years.
Thus it seems obvious to me that Bajor was civilized hundreds of thousands or millions of years ago, and that civilization fell, and the present Bajoran civilization arose merely tens of thousands of years ago.
But how could Bajoran artifacts and ruins survive on the surface of a planet with weather for hundreds of thousands or millions of years?
My theory is that modern Bajoran, Cardassian, and Federation archaeologists have found the remains of ancient Bajoran spaceships, space stations, space colonies, etc. in the Bajoran system and thus learned of the lost ancient Bajoran civilization.
And if the ancient Bajoran civilization was advanced enough to have interplanetary space travel, it could easily have been advanced enough to have discovered warp drive and left remains of it's activities in nearby solar systems, including the Cardassian system, thus giving Cardassians an inferiority complex and making them want to conquer Bajor.
Thus I think that the Bajorans were probably another society that once had warp drive and later lost it.
In "Balance of Terror" no one has ever seen a Romulan or knows what one looks like. Then they glimpse the Romulan bridge:
SPOCK: I have a fix on it, Captain. I believe I can lock on it, get a picture of their Bridge.
KIRK: Put it on the screen.
(Up shimmers an image of a group of four humanoids around a console. One leaves his post and salutes the figure with his back to us. That figure then turns, and we see someone who looks just like - a Vulcan. Both Spock's eyebrows hit the ceiling. There's a long silence and a lot of stares.) KIRK: Decoding? Blockquote
After that revelation, there is one suggestion about the possible origin of the Romulans:
SPOCK: Yes, indeed we do, Mister Stiles. And if Romulans are an offshoot of my Vulcan blood, and I think this likely, then attack becomes even more imperative.
MCCOY: War is never imperative, Mister Spock.
SPOCK: It is for them, Doctor. Vulcan, like Earth, had its aggressive colonising period. Savage, even by Earth standards. And if Romulans retain this martial philosophy, then weakness is something we dare not show.
Spock may have referred to Vulcan's aggressive colonizing period of planet bound expansion like during Earth's Age of Exploration and 19th century colonization. But if the Romulans might be a remnant of a period of aggressive colonization it must have been an aggressive colonizing period of interstellar expansion. [Did Earth ever expand and colonize aggressively in interstellar space in Star Trek long before the Federation?]
But Vulcan's civilization must have fallen sometime after Romulus was colonized. Otherwise when the Romulan War started the Vulcans would have known that the Romulans were the people of their colony number 37 who had revolted 152,246 Vulcan years ago and been fighting occasional wars with Vulcan ever since. There would never have been any mystery about Romulan origins.
The Fall of The Vulcan Space Empire many thousands of years ago caused civilization to fall on Vulcan, Romulus, and every other colony planet of Vulcans - otherwise any planet where Vulcan civilization hadn't fallen would have quickly rebuilt the Vulcan Empire and the rebuilt Vulcan Space Empire might still rule this part of the galaxy.
So Vulcan, Romulus, and other Vulcan colony planets rebuilt their civilizations independently in the millennia since the fall of the Vulcan star traveling society. And any Vulcan planets that invented any form of faster than light star travel - instead of learning the technology from other cultures - did so independently at different dates. And the only clue to the dates they might have invented warp drive is that it could not have been too many centuries or millennia before Earth did, or they would have had too much of a head start for Earth ever to become important and influential in interstellar affairs.
McCoy might mention The Fall of the Vulcan Space Empire and the fall of ancient Vulcan civilization in "Conscience of the King":
MCCOY: Negative. Did you know this is the first time in a week I've had time for a drop of the true? Would you care for a drink, Mister Spock?
SPOCK: My father's race was spared the dubious benefits of alcohol.
MCCOY: Now I know why they were conquered. What are you so worried about, anyway? I find Jim generally knows what he's doing.
Since McCoy doesn't mention the date of the alleged conquest, he might be referring to the Fall of the Vulcan Space Empire tens or hundreds of thousands of years ago. Why he thought sobriety could be a cause of being conquered is a mystery.
In "The Immunity Syndrome" Spock says:
SPOCK: Captain, the Intrepid would have done all these things too, and yet they were destroyed.
KIRK: Well, they may not have done all of these things. You just pointed out how illogical this situation is.
SPOCK: True. It is also true they never knew what was killing them. Their logic would not have permitted them to believe they were being killed.
SPOCK: Vulcan has not been conquered within its collective memory. The memory goes back so far that no Vulcan can conceive of a conqueror. I knew the ship was lost because I sensed it.
I speculate that the collective memory of Vulcan goes back thousands, tens of thousands, or even hundreds of thousands of years, but does not go back to the time of the Fall of the Vulcan Space Empire, and the existence and fall of the lost Vulcan interstellar society is known only from archaelology.
In "Journey to Babel" :
MCCOY: I see it, Spock, but that was a Rigelian.
SPOCK: Rigelian physiology is very similar to Vulcan.
MCCOY: Similar is not good enough. It's still experimental.
Maybe the natives of Rigel V are merely similar to Vulcans and maybe they are descended from a lost Vulcan colony and have gradually evolved differences from Vulcans in tens or hundreds of thousands of years of isolation from Vulcans.
In "The Paradise Syndrome" Spock studies the writings of the Preservers:
SPOCK: You prescribed rest, Doctor. The symbols on the obelisk are not words. They are musical notes.
MCCOY: Musical notes? You mean it's nothing but a song?
SPOCK: In a way, yes. Other cultures, among them certain Vulcan offshoots, use musical notes as words. The tones correspond roughly to an alphabet.
So Spock knows of two Vulcan offshoot cultures that use musical notes as words, as well as other Vulcan offshoot cultures that done't use musical notes as words. Thus Spock should know of at least three or four Vulcan offshoot cultures, and they may be descended from the time of Vulcan's aggressive interstellar conquest and colonization. Thus Spock may have good reasons to suppose the Romulans descend from a planet colonized during that period.
In "The Enterprise Incident" Kirk asks the Romulan Commander:
KIRK: What earns Spock your special interest?
COMMANDER: He is a Vulcan. Our forebears had the same roots and origins. Something you wouldn't understand, Captain. We can appreciate the Vulcans, our distant brothers. I have heard of Vulcan integrity and personal honour. There's a well-known saying, or is it a myth, that Vulcans are incapable of lying?
Do the Romulans know of their Vulcan ancestry because of historical knowledge passed down the ages since Romulus was settled by Vulcans, or have they learned that the natives of Vulcan are similar to Romulans and then had their spies investigate until they were certain that Romulus must have been founded by Vulcan?
In "The Savage Curtain" the image of Surek mentions Vulcan history:
SURAK: In my time on Vulcan, we also faced these same alternatives. We'd suffered devastating wars which nearly destroyed our planet. Another was about to begin. We were torn. But out of our suffering some of us found the discipline to act. We sent emissaries to our opponents to propose peace. The first were killed, but others followed. Ultimately we achieved peace, which has lasted since then.
This suggests that in the time of Surek Vulcan had many atomic weapons. If so Vulcan might also have had interstellar travel and a space empire. But there is certainly no evidence that Vulcan was more advanced than late 20th century AD Earth in Surek's time.
It seems more logical to believe that the Romulans are remnants of an ancient Vulcan Space empire countless thousands of years and that Vulcans, Romulans, and other Vulcan offshoots rebuilt their civilizations many thousands of years after the fall of the Vulcan space empire, than to believe that Vulcan has had star travel continuously since the time of Surek and yet the Vulcans have failed to become dominant in local interstellar affairs.