Asgard-Replicator war

The Asgard-Replicator war was was a conflict which nearly saw the extinction of the Asgard.

After discovering the Replicators on a planet in the Ida galaxy, the Replicators were quickly able to assimilate Asgard technology and become a serious threat to the Asgard. The Asgard responded by making more advaced technology, which the Replicators simply assimilated and became resistant to. For some time, the Asgard Fleet, under the command of Supreme Commander Thor, were able to hold the Replicators off, and still use some resources to combat the Goa'uld. Eventually, however, the tide began to turn in the Replicators favor.

The Asgard's alliance with the Tau'ri proved extremely beneficial to Asgard. Their guns were able to effectively terminate Replicator blocks, and their strategies were able to counter the Replicators. Samantha Carter's idea to use the O'Neill to lead three Replicators ships away from an Asgard homeworld was effective, and one the Asgard admittedly would never contemplate using. SG-1's discovery of the android Reese was able to further help the Asgard in combating the Replicators. However, the Replicators soon began to regain the advantage.

Eventually, the Asgard High Council devised a bold trap: using a single command code in the deactivated Reese, they activated it on the planet Halla. The code instructed the Replicators to converge on Halla. There, they hailed Reese as their creator, and found her nanite cells held significant advantages over the standard Replicator blocks. However, this was only part of the Asgard's plan. They used a time dilation device to slow down time within a radius of 0.16 light years by 10^4 power. Unfortunately, the Replicators were able to create a Human Form Replicator which was designated First. First was able to penetrate the device, made of neutronium, and reverse it, making time go faster. SG-1 was contacted, and they were able to reset the device.

The Asgard were aware that it would take the Replicators only two years outside the field to escape, so the Asgard artificially increased the mass of Halla's sun, causing it to collapse and become a black hole. Fifth, the sole surviving Human Form Replicator, lead the Replicators to Orilla, where the Asgard were attempting to rebuild their civilation. Colonel Jack O'Neill, who had downloaded the Ancient's repository of knowledge into his brain, devised a Disruptor that rendered the blocks and cells inert. Within a matter of months, the Replicators were forced to flee the Ida galaxy for a new location: the Milky Way. Eventually, a Carter Human form Replicator was able to develop a cypher to make the Replicators immune, and killed Fifth, taking control of the Replicators.

Eventually, the Replicators came into conflict with the Goa'uld Empire, seriously destablizing it. All the System Lords except Baal were killed, and the rest rallied under Baal. Upon learning of the power of the weapon on Dakara, Samantha and Jacob Carter were able to destroy every Replicator in the galaxy, ending their threat forever.