Simplify the following text for a Grade 10 native English-speaking person.
Original: Following Operation Ivy 's breakup , Tim Armstrong and Matt Freeman decided to form a new band , and started a hardcore punk group called Generator , which quickly broke up .
Simplified: When Operation Ivy broke-up , Armstrong and Freeman decided to form a new band , and formed a ska punk band called Downfall , which disbanded a few months . They then started a hardcore punk band called Generator , which also disbanded shortly after .