Defenders of Man: they staged the attacks

The Defenders of Man was a terran anti-Dominion separatist group whose stated intent was to protect humanity from alien threats. Secretly organized by General Carolina Davis, a Dominion general loyal to the Mengsk family, the group manufactured zerg attacks on Terran Dominion worlds in order to discredit Emperor Valerian Mengsk and seize power. Its campaign, the Defenders of Man Insurgency, was ultimately exposed and crushed through the efforts of the ghost Nova Terra. (StarCraft II: Nova Covert Ops)

Origins#

The Defenders of Man formed at some point after the End War and grew into a powerful anti-Dominion movement, arguing for the security of humanity. It was secretly organized by General Carolina Davis, a prominent Dominion general loyal to the Mengsk family, who obtained a recording implicating Valerian in the death of Arcturus Mengsk. (StarCraft II: Nova Covert Ops)

Unleashing the zerg#

In their early stages, Defenders of Man agents arranged for the transfer of several Dominion ghost agents, including Nova Terra and Stone, to aid the group's activities. Nova was sent to plant what she believed were anti-zerg devices in New Andasar on Antiga Prime, but the devices were in fact psi emitters set to attract specific breeds of zerg. Before Nova and Stone could escape, they were captured, and Davis subjected Nova to a mind wipe. (StarCraft II: Nova Covert Ops)

Nova later awoke with no memory in a Defenders of Man facility in Sharpsburg and escaped along with the captured ghosts Stone, Theodore Pierce, and Delta Emblock. Investigating further, she discovered that the Defenders were using psi emitters to attract feral zerg to Tyrador IX in a bid to make Valerian's regime appear ineffectual. (StarCraft II: Nova Covert Ops)

Heroes of the people#

The Defenders released psi emitters on Tyrador IX, luring feral zerg that overwhelmed the population, then arrived offering to evacuate civilians. Nova and her Covert Ops Crew followed. When the Tal'darim arrived under First Ascendant Ji'nara seeking vengeance for an earlier Defenders attack on a Tal'darim outpost, Nova destroyed the Tal'darim mothership to protect the civilians the Defenders were sheltering, and the Defenders rallied to repel the feral zerg. Credited with saving Tyrador IX, the group's membership grew. (StarCraft II: Nova Covert Ops)

Nova, meanwhile, struck a bargain with Highlord Alarak and used terrazine from Jarban Minor to recover her lost memories, finally remembering that General Davis was the Defenders' leader. She reported this to Valerian, who said he had a plan to stop them and that Nova needed to play her role to prevent further deaths. (StarCraft II: Nova Covert Ops)

The conspiracy collapses#

Valerian traveled to Vardona to announce, as a ruse, that he was stepping down as emperor. While the Defenders watched his convoy, Nova slipped through the sewers into Davis's compound, where she found the Defenders mind-wiping Dominion ghosts and developing new Dominion technologies. She incapacitated Stone, her old squadmate, and arrested Davis. Before the people, Valerian publicly decried the Defenders of Man and presented evidence of their crimes, but a Tal'darim Death Fleet then struck Vardona seeking revenge, and Davis escaped aboard a commandeered ship. (StarCraft II: Nova Covert Ops)

Davis fled to the Cerros Shipyards and activated the experimental war machine Xanthos, attempting to destroy the Dominion fleet's Gorgon-class battlecruisers. Nova and Admiral Matt Horner defended the Gorgons and destroyed the Xanthos, after which Nova found Davis alive in the wreckage and, in direct defiance of Valerian's orders, killed her. Public opinion returned to Valerian, but Nova became a Dominion fugitive, retaining the loyalty of her covert ops crew. The feral zerg attacks the Defenders had instigated on Tyrador IX led to the formation of the Knights of Tyrador as the planet's security force. (StarCraft II: Nova Covert Ops; StarCraft II War Chest)