- "Great holy armies shall be gathered and trained to fight all who embrace evil. In the name of the Gods, ships shall be built to carry the warriors out among the stars and we will spread Origin to all the unbelievers. The power of the Ori will be felt far and wide and the wicked shall be vanquished."
The Ori Crusade was a holy war that the human followers of the Ori waged against the races of the Milky Way in an attempt to convert the galaxy to Origin. It was instrumental in breaking apart the last vestiges of the System Lords, allowing the younger races to rise up and take their places as the new superpowers, though they would suffer incredible losses in the process. The conflict drove a noticeable wedge between the three major powers that had defeated the Goa'uld, but by its end, the Tau'ri, Free Jaffa, and Tok'ra were united once more.
Vala Mal Doran, Doctor Daniel Jackson, Lieutenant Colonel Cameron Mitchell, and Teal'c find the cavern below Glastonbary Tor and among the treasures, an Ancient Communications Terminal. Using the terminal, Vala and Daniel connect to two people in the Alteran Home Galaxy, but during their use of the terminal, expose the existance of people in the Milky Way to the Ori. Before they can be killed, the terminal they are hooked up to is destroyed which brings them back to their own bodies. The Doci declares a holy crusade on the people of the Milky Way Galaxy and promises that ships will be built to carry an army into the Milky Way. The Ori plan to gain as many followers as possible so they can become strong enough to face the Ancients in battle and destroy them. The Ancients refuse to interfer believing in free will enough that they will only interfer if the Ori take direct action.
In the meantime, while the army is being organized, the Doci sends Priors through the Stargate to convert Milky Way planets and gain more followers. If the planet refuses conversion, they're wiped out. The main tactic used is to spread the Prior Plague and cure people after they convert to make the Ori seem like Gods. If the people refuse to convert, the plague is allowed to run its course and wipe out the population. In an encounter with a Prior who spread the plague on a primitive village, the SGC fails to find a cure and the people are only saved because they convert to Origin as their religion.
- Main article: Battle of Kallana
As part of their plan to bring a fleet to the Milky Way, the Priors attempt to build a Supergate to bring the ships as the Alteran Home Galaxy is very far away from the Milky Way and it would take a long time to get there otherwise. The first attempt takes place at the planet of Kallana where they use the Goa'uld Nerus to trick to the Tau'ri into helping power their planet collapsing force-field with their weapons. The plan nearly succeds, but is foiled by Vala MalDoran who destroys the Supergate, but when she tries to ring back to the Prometheus, she is instead sucked into a black hole and sent to the Ori galaxy where she ends up in the rings of the village of Ver Isca and is found by a man named Tomin.
The Priors later make an attempt at converting or destroying Earth through the Prior Plague. However, an Ancient named Orlin decends to help find a cure to the plague. He helps finish a device that neutrilizes a Prior's powers and it is used to capture a Prior and get a blood sample in an attempt to find a cure. The attempt fails, but the Tau'ri learn from the Prior that the Ori are doing all of this to destroy the Ancients before Colonel Mitchell is forced to kill him. The attempt on Earth is foiled by Gerak who was turned into a Prior. He cures everyone in the SGC and using antibodies isolated from that, a cure is found, however, the act costs Gerak his life and Orlin his memories. The SGC spreads the cure to planets that need it, and even an alternate reality that desperatly needed a cure, and that method of attack is rendered useless.
- Main article: Battle of Tegalus
In converting the planet of Tegalus, the Priors use a different method: they give the Rand Protectorate a weapons satilite to use against their enemies as Rand wanted weapons technology to fight their enemy the Caledonians. The weapon proves powerful enough to destroy the Prometheus, although most of the crew manages to escape to Caledonia. The Caledonians are ultimatly given the Stargate so they can escape if they wish, but a war erupts and both sides destroy each other.
With their disease rendered useless, the Priors resort to using the bug R-75 on planets that are reluctant to convert. They are used on at least a few planets, but don't seem to be used often as they are only seen and mentioned once, so the Priors may have abandoned this method.
After the Sodan change their minds and turn their backs on Origin, a Prior turns the Sodan warrior Volnek into a kind of zombie that can only be killed through complete destruction of his body and unleashes him on the Sodan. Only Lord Haikon survives and Volnek is later killed by Cameron Mitchell and Teal'c. At the same time, Doctor Daniel Jackson discovers the existance of a weapon that can destroy Ascended Beings, created by the Ancient Merlin in order to destroy the Ori.
Using a second Ancient Communications Terminal, Vala MalDoran contacts the SGC through Daniel to warn them of the Ori fleet. She has been impregnated by the Ori in order to create a human representitive for them and has also joined the Anti-Ori Underground in order to do her part in resisting the Ori. After a plan by the leader Seevis to destroy the Ori motherships fails, Vala contacts Earth to warn them of the impending threat knowing that as the ships are leaving soon, there is another Ori Supergate in existance somewhere in the Milky Way. Vala is interrupted by her husband Tomin who kills Seevis and another member of the underground, but is convinced by Vala that she is innocent and to take her with him when he goes to war in the Milky Way. With this new information, the Tau'ri, the Tok'ra and the Free Jaffa begin a search for the Supergate while SG-1 begins a search for Merlin's weapon.
The Free Jaffa manage to locate the Supergate and a fleet of ships made up of Tok'ra and Free Jaffa Ha'taks and Al'kesh, an Asgard mothership, the Odyssey and the Korelev forms to try and destroy the Supergate, or failing that, stop any fleet that arrives. On the planet Camelot, SG-1 searches unsucessfuly for the anti-Ori weapon. They locate the treasure hidden there, but learn that the weapon which is called the Sangraal, is gone and find out the name of three planets where it could be located. Teal'c and Carter leave on the Odyssey and Teal'c goes to enlist the help of the Lucian Alliance while Mitchell and Jackson come later on the Korelev. At the Supergate, Carter attempts to dial out with Kvasir's help, but fails as the Ori dial in and send a fleet of four ships to the Milky Way.
- Main article: Battle of P3Y-229
The crusade began at the Battle of P3Y-229. At the activation of the Supergate, the Ori Army sent four Ori battlecruisers through it as a first wave. It battled two 304s, one O'Neill-class ship, and a fleet of Ha'taks from both the Free Jaffa Nation and the Lucian Alliance. However, their efforts were unsuccessful, as the Ori shields were too powerful for their weapons to pierce. When the battle ended, Vala Mal Doran, on one of the ships, gave birth to her daughter Adria, and learned that she was Orici, an Ori in human form intended to let the Ori lead the Ori army without enticing the Ancients
- Main article: First Battle of Chulak (Ori Crusade)
After leaving the system, the Ori Fleet travelled to Chulak, since the world was the first to denounce the Goa'uld. One ship landed planet side to launch a ground invasion, while the other three remained in orbit. Bra'tac brought three ha'taks to try and defend the planet, but they were destroyed. SG-1 and Bra'tac were rescued by the Odyssey, which had followed them once its hyperdrive was repaired, and Vala and Daniel Jackson (who escaped the Korelev's destruction by ringing to an Ori mothership) were also beamed aboard, saving them from a Prior which attempted to kill them. Over the next week, the Ori conquered six more worlds, including two Jaffa strongholds. 
- Main article: Battle of the Black Hole
In a plan to seal the Supergate, SG-1 travelled to Atlantis to cause a jump with a black hole, as well as locate the Sangraal, a weapon Merlin built to kill the Ori. While there, Daniel Jackson met the Ascended Ancient Morgan Le Fay, who told him of Merlin's intentions, and that she had taken the Sangraal and hid it on one of three worlds: Castiana, Sahal, and Vagonbrei. However, the Others prevented Morgan from telling him anything further. The plan to cause the jump eventually worked, and also resulted in the destruction of both an Ori battlecruiser and a Wraith Hive-Ship. 
- Main article: Devastation of Dakara
Suffering massive losses, the Free Jaffa, under Se'tak, used the Dakara Superweapon to destroy the crew of an Ori battlecruiser. Adria retaliated by destroying the weapon and devastating Dakara, fracturing the Free Jaffa Nation, thus removing the only organized military force that could effectively combat them. 
Eventually, SG-1 and the System Lord Ba'al discovered the location of where Morgan hid the Sangraal. After discovering Adria in their midst, they were transported to a planet where they learned that Morgan had destroyed the Sangraal, but hidden the real prize: Merlin, held in a stasis pod so that he could one day rebuild the weapon. Merlin agreed to help them, but his body had aged to much while in the pod, and he transferred his memories to Daniel Jackson. Daniel built two phases of the device, but Adria found where they were and captured Daniel and the weapon. Adria believed that she converted Daniel to Origin and made him a Prior of the Ori, but Merlin's conciousness was able to protect him. He made contact with SG-1, and convinced them and Jack O'Neill to shut down the Supergate so that he could send the weapon through. They succeeded, and but the Ori army regained control of the Supergate, sending another six ships into the galaxy. It is later revealed that the Sangraal did its job abd destroyed the Ori. 
SG-1 set a trap for Adria, but it was ruined when Ba'al kidnapped her and took her as a host. With the help of the Tok'ra, they removed Ba'al, but he released the symbiote toxin into Adria. Dying, Adria ascended. 
- Main article: Battle of the Asgard Legacy
When the Asgard realized that they were unable to repair the defects caused by their constant use of cloning, they decided to commit mass suicide and leave their technology and knowledge to the Tau'ri. The new weapons are capable of piercing the shields of the Ori battlecruisers. With this new technology, the Tau'ri are now a potential threat to the Ori fleet. 
Turning the tide
- Main article: Second Battle of Chulak (Ori Crusade)
- Main article: First Battle of Langara
- Main article: Battle of the Klan'nak Station
Earth and the Nox's return
- Main article: Battle of Earth (Ori Crusade)
- Main article: Battle of Hebridan (Ori Crusade)
- Main article: Assault on the Supergate
- Main article: Second Battle of Langara
- Main article: Battle of (unknown Jaffa planet)
- Main article: Skirmish at the Alpha Site (Ori Crusade)
End of the crusade
The crusade finally ended with the Ark of Truth, with a win for the humans of this galaxy. Morgan Le Fay began directing Daniel through dreams to search for the Ark of Truth, and Ancient device that will force the followers of the Ori to beleive the truth about them. SG-1 searchs the ruins of Dakara for it and apparently find it when they are captured by Tomin and his forces. SG-1 convince Tomin of the truth by killing the Prior he's with (the Prior disruptor is secretly blocking his powers) and he helps them figure out that the Ark is likely in the Ori galaxy. Also the team learns that the Ori may now be coming after Earth. In an attempt to stop this, the team and Tomin takes the Odyssey to the Ori galaxy through the Supergate to find it and stop the Ori forces.
There they found out that the Ori are indeed dead but Adria has taken all of their power and is planning to concur the universe and destroy the Ancients. The IOA tries to implement a plan to use the Replicators to destroy the Ori forces but things go bad until Colonel Carter manages to trigger a self-destruct in the Replicator forces. The crusade finally ends when Daniel, Teal'c and Vala activate the Ark forcing the Ori followers in the Ori galaxy to realize the truth severly diminishing Adria's power. Morgan Le Fay engages her in battle and the two apparently destroy each other. SG-1 takes the Ark back to the Milky Way where they use it to convince the Priors of the truth there as well ending the crusade. 
With the end of the crusade, the Milky Way Galaxy was at peace once again. SG-1 started heading out on normal reconissance missions and the Ori Army returned home under the command of Tomin, their new leader. At some later point, Ba'al was finally tracked down and killed, and with his death and the end of this crusade all known threats in the Milky Way were gone... for the time being.
- Battle of Kallana
- Battle of Tegalus
- Battle of P3Y-229
- Battle of the Black Hole
- Battle of the Asgard Legacy
- Battle in the Alteran Home Galaxy
- Tau'ri-Ori skirmishes