Division X was a CIA division designed to take down Sebastian Shaw and his Hellfire Club. Although the CIA shut down the division, it was not formally disavowed until after the Cuban Missile Crisis. Following this, all history or knowledge of the division was kept a secret until 2013.
Division X was approved by CIA senior executive, known as the Man in Black. He approved of the request of Moira MacTaggert to give Charles Xavier a team of mutants with which to fight the Hellfire Club. Soon after, Xavier was joined by Erik Lehnsherr and with his sister, Raven Darkholme, recruited several young teenaged mutants. After an attack on the CIA by the Hellfire Club, Division X was to be shut down, with one member dead and another defected to the Hellfire Club. However, the remanining members of the team relocated to the Xavier Estate where they continued their training. Eventually, Divison X participated in the Cuban Missile Crisis, where they prevented a worldwide nuclear conflict. Shortly after the battle, Lehnsherr created the Brotherhood of Mutants with Darkholme and several Hellfire Club members. Divison X was formally disbanded three days later.
Xavier went on to found the Xavier's School for Gifted Youngsters. In 2005, he used select mutant teachers, former students, to form another task force similar to Division X. This squadron began to be known as the X-Men and fought against threats to the mutant community.