The Jedi and Sith have been been arch enemies ever since the latter was formed on Korriban,
and they have been involved in countless wars against one another for thousands of years.
But despite all these conflicts and need to defeat each other, there have been a few occasions
where the Jedi and Sith did actually team up and work together against a common enemy.
One notable occasion of this occurred during the Galactic War, in which the reemerged Sith
Empire fought to conquer the galaxy from the Old Republic.
During this war, a new force called the Order of Revan, also known as the Revanites, emerged
from the shadows and became a great threat toward both the Sith Empire and the Jedi led
Republic.
The Revanities were a cult that followed the returned dark-side embedded Revan.
Revan was on a quest to bring back the earlier defeated Sith Emperor Vitiate, in an attempt
to permanently kill him so Vitiate would be unable to transfer his consciousness as a
means to cheat death as he had done so many times before.
Believing both the Republic and Sith Empire would attempt to stop him, Revan tried to
destroy the two galactic governments but ultimately failed.
Despite this he still continued with his plans to bring back Vitiate in order to permanently
kill him.
Finding out what he was up to and believing what he was trying to accomplish was going
to do more damage than good to both sides of the war, both Republic and Sith Imperial
forces were sent to go stop him.
Although this brief alliance between the Jedi and Sith aligned forces was very shaky, with
both sides spying on one another during their team up, they were successful in defeating
Revan and his Cult Order.
The next alliance between them however ended up being much more intertwined and lasted
far longer, as both the Sith Empire and Republic were forced to forge an official military
organization called the Eternal Alliance in order to combat the Eternal Empire.
The Eternal Empire was secretly created by the former Sith Emperor Vitiate, now renamed
as Emperor Valkorion, who was onset in destroying and consuming all the life forces in the galaxy
as a means to become a god like being.
The Eternal Empire successfully became the dominant power in the galaxy and was later
taken control by Valkorion’s children.
Not wishing to being completely wiped out for good, the Sith and Jedi came together
with their respective military forces and fought against the Eternal Empire, successfully
overthrowing it in the end.
Funny enough, shortly after their victory the Jedi and Sith restarted their war against
each other.
The next notable Jedi and Sith team up wouldn’t happen for thousands of years, not until Abeloth
appeared in the galaxy.
Abeloth was an immensely powerful force being who was once The Mother of the Ones before
her downfall into insanity after she consumed both the light and dark side force nexuses.
She was imprisoned for thousands of years by The Ones who were forced to deal with her
every hundred or so years by reinforcing her restraints to a planet, but after they were
all killed following Anakin’s confrontation with them, there was no one to stop Abeloth
from being released into the known galaxy after her she figured out how to escape her
prison.
Abeloth was so powerful that even Grand Master Luke Skywalker was unable to fully contented
with her, and even the Lost Tribe of Sith that fought her as they initially attempted
to control her found her to be far too overwhelming.
Even when they blasted her with force lightning she reacted as if they were tickling her.
Abeloth was also able to appear as anything she pleased, from demented tentacle like monsters
to beings her enemies knew personally.
She was eventually defeated by Luke Skywalker and a forthcoming Sith Lord named Darth Krayt.
Although initially it was a 3 way battle, Krayt and Luke eventually came to an understanding
that they needed to work together if they had any chance of defeating Abeloth.
And they barely were able to do just that, with both of them being pushed to their absolute
limits and facing multiple near death experiences during their fight against her.
There were a few other moments where the Sith and Jedi briefly teamed up to overcome a common
goal.
For example, when Anakin, Obi Wan, and Dooku worked together to escape Hondo’s prison.
But nothing as major as the ones we mentioned earlier.
Also while the Sith were not around during the Vong invasion of the galaxy, it’s very
likely that if they were, they would have eventually teamed up with the New Jedi Order
to fight against the galactic invaders.