The Splicer Purge was an infamous event in Rapture history taking place shortly after Jack's rampage through the city.
After the death of Fontaine and the harvesting of the Little Sisters, Jack begins to rule the broken city of Rapture. His extensive power allows him to not only hypnotize Big Daddies but keep them permanently under his control aswell as Little Sisters. With them, Jack begins to harvest ADAM for himself in vast quantities.
Unfortunately, his slaves begin to fall prey to strrong Splicers so Jack begins Hypnotizing other Splicers and Big Daddies for the sole purpose of hunting down and killing off all Splicers. His forces patrol the halls with precise vigilance, shooting down anything that even looks insane.
Jack's Hypnosis over these death squads lasts for only a limited time due to lack of ADAM and EVE in Rapture. Shifting his focus from the Splicers and returning to the harvest, Jack leaves the remnants of his Death Squads in the bowels of the city to hunt down cowaring Splicers on their own. Eventually, as ADAM begins to run scarce, Jack looks to find other ways for ADAM.
He has Big Daddies capture Splicers and begins a range of experiments on them to increase the amount of ADAM they hold 10 fold. This works for a bulk of Splicers but the majority begin to die off. Eventually, Jack begins to lose control of his powers and when Eleanor becomes enters the scene as a young woman, Jack is eventually overthrown.
Despite this, many of the Big Daddies once Hypnotized by Jack for long periods of time remain with a deep will to eradicate Splicers. For years the Big Daddies shoot, explode, impale, and crush any Splicer in Rapture. During this time, over 60% of Raptures population was lost to rampaging Big Daddy armies. It took nearly a decade for the Hypnosis to fully wear off.