While Gotham was under siege, former Titan Victor Stone (aka: Cyborg) saw a need for a team of heroes that would handle any crisis that occurred in cities without a dedicated protector or who could investigate other matters of concern without violating the U.S. government ban on the JLA acting in international affairs. So he set up shop inside an old secret training and meeting facility that the ‘super friends’ used to use, in the quiet East Coast town of Happy Harbor. This secret team was never given a name, but Cyborg liked to call it ‘Young Justice’ on account of most of its members being teenagers and young adults.
The team's first recruits were Kid Flash (Wally West), Wonder Girl (Cassandra Sandsmark) and Aqualad (Jackson Hyde). With the Justice League of America and the Titans disbanded (in the aftermath of Jason Todd's death), the sidekicks didn't have a place to go for further training, so Cyborg took them in.
Their first mission was to investigate a fire in Cadmus Labs, where they eventually found and rescued Superboy. Accidentally freeing Bizarro too. Superboy was assigned to the team, and given his mental instability due to him being a clone, Miss Martian was assigned as his psychic handler and given a position on the team too.
After Gotham City was under control again, Batman sent Robin (Tim Drake) and Batgirl (Cassandra Cain) to join the team; and eventually a new Speedy (Artemis Crock) joined too, after Green Arrow decided he didn't have time to train a new sidekick because he was too busy mourning the first Speedy, Roy Harper (and avenging him).
Among their missions, the Team was the first to discover the criminal organization known as The Light.
After the Justice League was reestablished under the U.N and ARGUS supervision, Titans Tower was reopened and the Team was reorganized as the Third Generation of Titans, with Cyborg as the headmaster and other members of the Justice League acting as teachers from time to time.