The Dent Act was a law that was passed after the death of Harvey Dent. It was a law that was so effective that it wiped out organized crime by locking up all 1000 criminals in Gotham City for eight years after the Joker's reign of terror upon Gotham City as well as the death of Dent himself. The law, in part, allowed for gender separation in prisons to cease as well as create stricter penalties. Its main feature denied parole to the men Dent's prosecution locked up. Thus, all the 549 mobsters Dent locked up would be off the streets for good, along with any criminal that tries to restart the organized crime machine.
The Dark Knight Rises
- "Behind you stands a symbol of oppression. Blackgate Prison, where a thousand men have languished under the name of this man, Harvey Dent, who has been held up to you as the shining example of justice! You have been supplied with a false idol, to stop you from tearing down this corrupt city! Let me tell you the truth about Harvey Dent from the words of Gotham’s police commissioner, James Gordon. 'The Batman didn’t murder Harvey Dent, he saved my boy. Then took the blame for Harvey’s appalling crimes so I could, to my shame, build a lie around this fallen idol. I praised the madman who tried to murder my own child, but I can no longer live with my lie. It is time to trust the people of Gotham with the truth, and it is time for me to resign.' And do you accept this man's resignation?"
The importance of Dent's prosecution 8 years ago was that he locked up 549 of the 1000 criminals in Gotham. And this was important since the 549 men was the whole mob, for Lau told the mob, "everyone's money would be at stake", since they laundered all of their money to him. Since Lau turned over all his clients in Harvey's RICO case, Dent would end up locking up the whole mob, allowing law enforcement to easily deal with the remaining street criminals; hence why Dent told the mayor that he will now have "18 months of clean streets". Because of that, the mayor was worried that after 18 months of jail, the mobsters would try to use any dirt found on Harvey to appeal and undo the prosecution so "[these] criminals would be back on the streets". Then, the mob leaders used bail to get out of jail early and they hired the Joker. This caused a chain of events that resulted in all mob leaders dying and Joker burning the mob's whole money supply along with Lau. Since there was no dirt on Harvey from Batman taking the rap for his murder spree, the mobsters failed at appeal. With the Dent Act denying parole, the rest of the mob cannot get out of jail early and are forced to serve their full 20 year sentencing under RICO. As a result, organized crime didn't bounce back.
Bane stole a speech from James Gordon, which he read outside of Blackgate Prison, which was a revelation of what Harvey Dent did after he lost Rachel Dawes at the hands of the Joker's thugs. This definitely prompted the inmates of Blackgate to riot before they were "liberated" by Bane's men. They then joined Bane and Talia (who was under the guise of Miranda Tate) in their "revolution". After Batman and the GCPD took Gotham back, the Dent Act was then eliminated.