Complex sentence: S.E.S. was the first highly successful female K-pop group, although they did not survive unchallenged: groups like Fin.K.L and Baby V.O.X debuted soon after S.E.S. and were also successful.
Split into simpler sentences: S.E.S. was the first highly successful female K-pop group. Although they did not survive unchallenged: groups like Fin.K.L and Baby V.O.X debuted soon after S.E.S. and were also successful.