Simplify the following text for a Grade 14 native English-speaking person.
Original: The latter act prompted Arnold to join the chorus of voices in opposition to those taxes , and also led to his entry into the Sons of Liberty , a secret organization that was not afraid to use violence to oppose implementation of those and other unpopular Parliamentary measures .
Simplified: The latter act prompted Arnold to join the opposition to those taxes , and also led him to join the Sons of Liberty , a secret organization that was not afraid to use violence to oppose those and other unpopular Parliamentary measures .