Simplify the following text for a Grade 9 native English-speaking person.
Original: Allied troops during World War II called massed infantry attacks by the Imperial Japanese Army , `` banzai charges '' or `` banzai attacks '' because the assaulting Japanese infantrymen yelled `` Banzai ! ''
Simplified: A Banzai charge ( or `` banzai attack '' ) ( è æ ç æ ' ) was a tactic used by Japanese soldiers against American soldiers when they were losing World War II . Banzai charges were usually suicide charges .