前史 is read as ぜんし (zenshi) and means prehistory.
ぜんし
zenshi
ぜんしじだい
prehistoric period
しじょうくうぜん
unprecedented in history
ゆうしいぜん
prehistory
れきしいぜん
prehistoric
まえぶれ
advance warning
まえわ
front wheel
ぜんやさい
event held the night before another event
ぜんれき
personal history
ぜんせん
(weather) front
ぜんしん
antecedents
まえうりけん
ticket sold in advance
ぜんりゃく
dispensing with the preliminaries ...