Profiles
KARA originally debuted with four members, Park Gyuri, Han Seung Yeon, Kim Sung Hee, and Jung Nicole. The group debuted on March 29, 2007 with "Break It!" on M! Countdown. With their first album, "The First Blooming", the group had a more mature image and focused on singing and music instead of appearing on variety shows.
In March 2008, Kim Sung Hee suddenly left the group due to parental pressure. Her participation in the group depended on her grades and she failed to pass her college entrance exams, and as a result, was forced to leave the group.
KARA made a comeback on July 24, 2008 with two new members, Koo Hara and Kang Ji Young, performing their song "Rock U" off of their new mini-album, with more of a "cute" image.
They released their second mini-album, "Pretty Girl", on December 4, 2008 and a re-packaged edition of the mini-album, entitled "Honey" was released on January 18, 2009.
(Information from Wikipedia and Google and re-worded a tad by me. =P)