Black Lanterns were the resurrected forms of various deceased creatures and people that were simultaneously raised from the dead by the will of Nekron, Lord of the Unliving, in order to carry out the Blackest Night and destroy all life and light, so that the universe would go back to being dark and dead again. All Black Lanterns are in some form or another, dead.
Both Corps were temporary for that event. The Black Lanterns functioned until Nekron was defeated, and then a smaller group of them operated into the Brightest Day until being defeated. The White lanterns too only appeared in order to defeat Nekron, and then to renew Swamp Thing during the Brightest Day storyline, after which both Corps. mostly vanished.