For how long were the Shadows and Vorlons at war with each other?

I always thought that the historical chronology of Babylon 5 is rather inconsistent.

The universe is believed to be over 13,000,000,000 years old, and if I remember correctly that was also the scientific belief when MJS was creating the basic plot for Bablyon 5 sometime back in the 1980s.

Humans consider themselves and their immediate ancestors to be the first species of intelligent life to ever evolve on Earth. Earth was formed about 4,600,000,000 years ago, and developed an oxygen rich atmosphere suitable for large, multi celled land animals to breath when it was about 4,000,000,000 years old.

And it seems perfectly possible that a star system with planets could have formed 8,600,000,000 to 9,200,000,000 years ago with just as much heavy elements as our solar system and planets have,and intelligent life could have evolved on one of the planets 4,600,000,000 years ago.

And it is possible that the first intelligent beings might have evolved on various planets in the universe 5,000,000,000, or 6,000,000,000, or 7,000,000,000, years ago.

The Vorlons and the Shadows are two species of the First Ones, the earliest intelligent beings in the universe. The first First One was allegedly the immortal Lorien, the first of his species.

Lorien makes the statement that he is not a First One but rather the First One, belonging to a nearly immortal race of great wisdom and power, and, according to himself, the first being to achieve sentience in the universe.[52] It was his race that discovered and nurtured many of what the Humans and Minbari refer to as the First Ones, including the Vorlons and the Shadows.

https://en.wikipedia.org/wiki/List_of_Babylon_5_characters#Lorien[1]

Lorien claims that "the universe" created him as an immortal intelligent being, but later switched to creating mortal intelligent beings.

Since intelligent being could have evolved in other star systems billions of years ago, and since Lorien claims that "the Universe" created him and some of the other intelligent lifeforms deliberately, and thus possibly long before it was possible for intelligent beings to evolve naturally, it is possible that the First Ones, including the Shadows and the Vorlons, have existed for five or ten billion years, for example.

Suppose that the Shadows and the Vorlons began fighting their proxy wars "only" one billion, or 1,000,000,000, years ago.

If the average interval between those wars was one million years, they would have fought one thousand such wars, with only the latest three known to characters in Babylon 5.

If the average interval between those wars was one hundred thousand years, they would have fought ten thousand such wars, with only the latest three known to characters in Babylon 5.

If the average interval between those wars was ten thousand years, they would have fought one hundred thousand such wars, with only the latest three known to characters in Babylon 5.

If the average interval between those wars was one thousand years, they would have fought one million such wars, with only the latest three known to characters in Babylon 5.

And I can't help thinking that the more such proxy wars that were fought, the greater the probability would be that the younger races would have thought of telling the Shadows and Vorlons to go away and leave them alone. It seems to me highly improbable that the Shadows and the Vorlons would still be at it after hundreds or thousands of such proxy wars.

The fact the Shadows and the Vorlons are still fighting proxy wars in the era of Babylon 5 makes me suspect that the war about 10,000 earlier might have been the first war, or second war, or third war, or something. I find it hard to believe that the Shadows and Vorlons have been fighting proxy wars via the younger species for hundreds of millions, or billions, of years.

Anyway, I find the historical chronology of babylon 5 to be rather vague and insistent, and so I doubt that anyone, not even MJS himself, can give a good answer to the question of how long the Shadows and Vorlons were at war.

Sorry this has conjecture but i am confident it is accurate. See link for a quote. How did Kosh know to tell Sheridan to jump into the abyss on Z'ha'dum?

Lorien moved into the pit on Z'ha'dum a million years ago. One can assume that was when his race as parents of the first ones stopped participating in events and the First ones took over the role of parenting.

Prior to that I would assume the wars were between the shadows and other first ones. The shadows being the first race Loriens species found. The conjectured wars between the first ones could go for billions of years. I would speculate the shadows viewed themselves as helpful older siblings. And I'd speculate the rest of the first ones considered them older bullies. Then when Lorien left and the first ones were all technologically equivalent the sibling rivalry switched to proxy wars and guidance of the humanoids.

We discovered the Vorlons and the Shadows when they were infant races. And it nourshired them, helped them and all the other races you call the First Ones. In time most of them died, or passed beyond the rim to whatever lies in the darkness between galaxies. - Lorien "Into the Fire"

Note regarding "it nourished" the larger context is about the universe deciding against immortality. So he probably could have said "evolved" here.

The last great war 10 thousand years ago was when the majority of the first ones left for the rim. https://babylon5.fandom.com/wiki/Last_Great_War I'd assume none of the humanoids participating in this one managed to keep their civilization progressing. Only the Minbari seemed to have succeeded in participating in two Shadow Wars (Valen and Sheridan's wars) and they are the oldest humanoids in the Babylon 5 time period. I'm confident the Minbari did not participate in the war 10,000 years ago - but it is not impossible.

"We have no other name for them. The Shadows were old when even the Ancients were young. They battled one another over and over, across a million years. The last great war against the Shadows was 10000 years ago. It was the last time the Ancients walked openly among us. But the Shadows were only defeated .. not destroyed. 1000 years ago, the Shadows returned to their places of power, rebuilt them, and began to stretch forth their hand. Before they could strike, they were defeated by an alliance of worlds, including the Minbari .. and the few remaining First Ones who have not yet passed beyond the veil. When they had finished, the First Ones went away .. all .. but one." -- Delenn in Babylon 5:"In the Shadow of Z'ha'dum"

The last Shadow war with Valen 1000 years ago only the Vorlons are actively manipulating the humanoid races anticipating the next war with the shadows. And during Babylon 5 the sibling rivalry got so hostile it became the final war. Lorien interceded and all the First Ones left. This left the advanced space faring humanoids to be the parents to the newer ones for the next million years. Eventually the Minbari and humans transcended and presumably will go beyond the rim themselves someday.

ADDENDUM: We can also assume that the million years the first ones spent being parents was mostly spent creating humanoids. We know that there is a population of telepathic Homo erectus on a Vorlon world. See Official Babylon 5 Magazine #24 (Aug 2000): The Nautilus Coil by J. Gregory Keyes

There is no canon source on this.

When we do get inside the head of someone who might know (mostly snippets of Kosh in the tie-in novels) they are focused on current events.

The most information that can be gleaned comes from characters like Lorien, who, in theory, were there.

• The First Ones arose.
• Most of the First Ones left, some stayed behind, and the Vorlons and Shadows stayed behind specifically intending to guide younger races.
• At some undefined point, "guiding" becomes "proving the other guy wrong".
• At some undefined point, "proving the other guy wrong" turns into a proxy war.

Since we have no idea when any of these events in particular happened in relation to each other, or even have enough context to define the specifics of those last two, there is no reasonable speculation that can be drawn.

So we don't know.