Used by the Lights at first to prevent intelligent life forms from becoming violent, but evolved into a process to make them more obedient and controllable.
The First Time
The first correction the Lights ran had no resemblance to their last corrections. One Light encountered two tribes of a very primitive life form who were constantly competing to hunt in the same area. As the hunters from both tribes began attacking the other group, the Light intervened when they began killing each other. Using its own mind, the Light joined the minds of the two groups to allow them each to experience what the other group felt during the attack. This resulted in the two tribes realizing they were no different from each other so they grouped into one larger tribe. The Light continued doing this with any other tribes it found doing similar things. Lights on other planets eventually heard about those events and tried doing the same thing.
Harder to Control
As a species population grew and became more intelligent, so did the conflicts and their complexity. When thousands of life forms began fighting, it was impossible for a single Lights mind to stop them all and link their minds. They decided to physically separate any warring tribes, while a handful of Lights would link the minds of their leaders. But when millions began to fight, using guns, canons, or even more advanced weaponry, there were not enough Lights to separate and control the groups.
The population growth led the Lights to develop a new type of string which could detect violent life forms and isolate them from the others. At first they would hold everyone on both side until they could convince the leaders there were better ways of handling the situation. But as species grew in intelligence, they also grew in stubbornness.
With the leaders of most life forms no longer immediately seeing thinks the Lights way, they believed they had no other way but to hold both sides in settlements and teach them all a better way to live. Most life forms saw the settlements they were kept in as prisons. They only cooperated in hopes they would be released one day. The result was a generation or two of life forms restraining their violence, only because they did not want to be imprisoned again. But after a few generations, the settlements would be forgotten and the life forms would revert back to their old behavior.
Ten Thousand Year Disaster
When the Lights gathered to deal with the Dren almost all planets in the galaxy were left with nobody to watch over them. On Earth, Human evolved from nomadic tribes to huge cultures of billions. All with weapons advanced enough to destroy a planet. Earth was not alone. The Lights were horrified to find most of their home planets had turned into either wastelands or permanent battlegrounds. They attempted correction over and over, failing faster each time they tried. They began to believe the only species who were not affected were their allies such as the Juvo. But they soon realized even their allies had changed. When the Juvo revolted, Core requested all the Lights in the galaxy to return to help find a way out of the situation.