Here a brief summery of the Histroy of SHadowClan in each book.
Into The Wild
ShadowClan had already driven out WindClan under the leadership of Brokenstar. Clawface and a few other ShadowClan cats tried to steal the ThunderClan kits and killed Spottedleaf. Firepaw, Greypaw, Yellowfang, Nightpelt and a few others attacked ShadowClan and took back the kits and freed the Clan of Brokenstar.