It started out as a social experiment, trying to see if there was a way to avoid another great war such as that which had most recently laid waste to the planet, toppling its cities, killing millions, and irradiating its lands. In all, five different groups raised their voices, each blaming some bad trait of humanity for the terrible conflicts; selfishness, cowardice, ignorance, duplicity, or simple belligerence. Five voices - Five Factions.
Another group believed the only way to find peace was to embody all the good traits; selflessness, courage, knowledge, honesty, and harmony.
With any experiment it needed to be self-contained so they built a high wall surrounding one of the few cities still left standing - Chicago - and locked the people inside, letting them believe there was nothing beyond the wall other than wastelands. The leaders were given a key that would bring the experiment to its natural close but within a few generations there was no one left to remember how it had once been and the Five Factions became their way of life. Nuture over Nature, with each person taking an aptitude test once they became of age that would determine which of the five voices ruled their hearts and minds.
Generation after generation, with those who watched the progress of the experiment looking for those who heard more than one voice.
No one expected the experiment to go awry, with the very people they sought - the Divergent - being treated as abnormalities who had to be cast out or eradicated for the good of the Five Factions. Yet it was inevitable that one of the Factions would abuse its position eventually, and destroy the delicate balance between the Five.
As Erudite used brainwashed Dauntless to murder the Abnegates the experiment was deemed a failure, and like with all failed experiments a decision was made to destroy the test environment and start again.
One recalled a quote by a long dead scientist: Too little knowledge is a dangerous thing. So is a lot.
What they had to decide before they restarted the experiment was whether Erudite had gained too much knowledge over the years set apart from the rest of the world... or simply not enough.