I was watching TNG : The Best of Both Worlds, Part 2. The Battle of Wolf 359 resulted in over 11,000 Federation deaths and the loss of a Borg Cube with its crew of thousands of drones.

This led me to thinking, what is the bloodiest war involving the Federation?

  • it was one of the battles in the dominion war i believe, checkout the dominion war page on memory alpha en.memory-alpha.org/wiki/Dominion_War
    – Himarm
    Commented Nov 21, 2014 at 21:13
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    and do you want war or battle?
    – Himarm
    Commented Nov 21, 2014 at 21:14
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    Do you count alternate/erased timelines? The Population memory-alpha article mentions that in the Federation-Klingon war seen in the timeline of "Yesterday's Enterprise", the Federation had suffered 40 billion casualties from 2344-2366.
    – Hypnosifl
    Commented Nov 21, 2014 at 21:30
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    Until Voyager undermines the incursion calculations in the Delta Quadrant done by the Krenim Imperium, the timeship destroyed countless civilizations whose number defied calculations. 5000 parsecs of space were erased and over 8000 civilization were affected. Commented Nov 21, 2014 at 23:30
  • @thaddeus - except that it was all just a dream :-)
    – Valorum
    Commented Nov 22, 2014 at 9:30

3 Answers 3


The Dominion War - Over 1 billion

Nearly a billion Cardassians and an unknown (but high) number of Federation citizens, Klingons, Romulans, Jem Hadar and Breens died in the Dominion war.

For the record, the largest set of casualties resulted from an attack by the Jem Hadar on their own former allies, the Cardassians.

The Borg invasion of Earth - 9 billion

The Borg invasion of Earth seen in Star Trek: First Contact is known to have resulted in over 9 billion humans being assimilated into the Collective.

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Federation / Husnock skirmish - 50 billion

In 2366, a Husnock warship destroyed the Federation colony on Delta Rana IV. Unbenknownst to the Husnock (and the colonists), one of the inhabitants happened to be an energy being known as a Douwd. The colonists fought and died at the hands of the Husnock and in retaliation, the Douwd destroyed the entire Husnock civilisation, a body-count of some 50 billion lives

KEVIN : No. You don't understand the scope of my crime. I didn't kill just one Husnock, or a hundred, or a thousand -- I killed them all. All! The mothers, the babies, all the Husnock everywhere! (beat) Are eleven thousand people worth fifty billion? Is the love of a woman worth the destruction of an entire species... ?

The Klingon/Federation War - 40 billion

In the alternate timeline created by the Enteprise-C in TNG: Yesterday's Enterprise, we learn that the Klingon/Federation War has resulted in the deaths of over 40 billion people (hat tip to @hypnosifl for reminding me):

PICARD : Not good enough. Not good enough. I will not ask them to die.

GUINAN : (softly) Forty billion have died in the war...

The Borg invasion of the Alpha Quadrant - 63 billion

Moving further down the canon scale, the EU novel Lost Souls focuses on an invasion of the Alpha Quadrant by the Borg. Although their plans are ultimately scuppered, the Federation takes casualties of over sixty-three billion lives lost, spread between the Federation, Romulan Star Empire and Klingon Empire. The conflict also resulted in the destruction of over forty percent of all Starfleet vessels.

  • After the Borg jumped to the past, the Enterprise crew saw an altered 24th-century Earth with a population of 9 billion, but those wouldn't necessarily all be long-lived drones made from humans assimilated in Zefram Cochrane's time, would they?
    – Hypnosifl
    Commented Nov 21, 2014 at 21:34
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    @Hypnosifl - I'm happy to agree that it's not made explictly clear whether the nine billion borg represent the population of Earth or whether they've used Earth as a regional hub for assimilation of the Alpha Quadrant
    – Valorum
    Commented Nov 21, 2014 at 21:42
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    @Hypnosifl - The borg don't breed; scifi.stackexchange.com/a/5661/20774 - We do know that the borg "homeworld" has over 50 trillion inhabitants. It's unlikely they all came from there in the first place.
    – Valorum
    Commented Nov 21, 2014 at 22:11
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    Uxbridge was not a Federation citizen. He was impersonating one.
    – Valorum
    Commented Nov 21, 2014 at 23:15
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    @Richard: To be fair, Uxbridge was on a Federation colony. The Husnock attack on that colony was therefore an act of war. A retaliation by Uxbridge might be considered part of the Husnock-Federation War. There's my Devil's Advocate quota for the day. Commented Nov 22, 2014 at 12:16

The bloodiest war in the Star Trek Universe was not in the Alpha Quadrant. The bloodiest battle was in the Delta Quadrant when the Borg fought against Species 8472.

  • Called the Borg-Species 8472 War the conflict lasted only six months and destroyed 8 planets, thousands of ships and millions of Borg drones. Species 8472 was superior in every way during this conflict.

Two examples of their obvious combat superiority came shortly after Voyager's initial foray into Borg space. In one engagement, a single 8472 bioship annihilated an entire fleet of 15 vessels with ease, which was the largest grouping of Borg vessels witnessed by a Federation ship up to that point. In a separate battle that occurred in Borg Matrix 010, Grid 19, the Borg lost eight planets, 312 ships, and 4,000,621 drones. The Collective's complete extermination was projected to be only weeks away. (VOY: "Scorpion, Part II")

  • The Borg lost thousands of ships, each ship capable of supporting hundreds of thousands of Borg. At least eight entire planets were lost in the struggle with Species 8472.

Species 8472 was the first species to offer "true resistance to the Borg." With their superior biological technology, Species 8472 was able to annihilate large numbers of Borg drones, ships and even planets.

Borg cubes were typically manned by "thousands of drones," and could vary in capacity anywhere from 5,000 to 64,000 to 129,000 drones. (VOY: "Collective", "Unimatrix Zero", "Dark Frontier")

  • It was these losses which lead to the compromise with Janeway and Voyager regarding the technology which would allow the Borg to effectively resist Species 8472.

While other conflicts in the Alpha Quadrant incurred massive losses, nothing even came close to the losses the Borg suffered and would have continued to suffer if not for the interaction of Voyager. Without the assistance of Voyager, it is conceivable the Borg would have been completely annihilated.

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    This may not be more than the 40 billion in @Richard's answer. Assuming "thousands of ships" to be 10,000, and all these ships to have 129,000 drones, we are left with 12.9 billion casualties. If all 8 planets the Borg lost had 9 billion Borg, as Earth did in the First Contact timeline, that gives an extra 54 billion dead. That totals 67 billion dead drones. Now, that is 27 billion more dead than in the aforementioned conflict, but that's a lot of assumptions to make, considering some Borg vessels have single-digit crews. And it's moot anyway, as the Federation wasn't involved in this war. Commented Nov 22, 2014 at 12:26
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    Voyager was the reason the war was won. Ergo the Federation WAS involved and instrumental in the winning of the conflict. Commented Nov 22, 2014 at 16:06
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    @Thaddeus - I'll agree that the Federation were involved. The numbers, however are pure guesswork.
    – Valorum
    Commented Nov 22, 2014 at 18:33
  • Indeed, but considering Borg planets can have widely diverse populations, it stands to reason, between the ship losses and the planet losses, that six month war was among one of the most devastating conflicts known. And given that some of the Borg worlds could have tens of billions of possible inhabitants, it should not be discounted as one of the largest losses of life in the known galaxy. I am certain the Federation was not upset to hear the Borg had suffered from such a devastating defeat. Commented Nov 22, 2014 at 19:57
  • @Thaddeus - The problem with trying to work out the numbers is that some borg colony worlds only have a few tens of thousands of inhabitants whereas some Borg worlds are known to have trillions of inhabitants.
    – Valorum
    Commented Nov 22, 2014 at 23:08

In one episode it was calculated that the Federation would lose the Dominion War and six hundred billion persons would be killed.

It is hoped that the war actually ended with only a tiny fraction of that number killed, but it still may have been far more than the number of Borg killed by Species 8472.

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    This doesn't answer the question in any meaningful way. They were talking about a potential war simulation, not real-worl casualties.
    – Valorum
    Commented Mar 26, 2015 at 0:41
  • Richard - they were trying to predict the actual future outcome of the war. If unexpected events ended the war with only ten percent of the casualties they predicted that would be sixty billion people, and so on. If some people seriously predicted six hundred billion dead in the Dominion war, it is perfectly possible that the actual casualties were greater than the sixty seven billion Borg who might have been killed in the war with Species 8472 according to James Sheridan. Commented Mar 28, 2015 at 6:05

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