Simplify the following text for a Grade 10 native English-speaking person.
Original: The Crisis began with the assassination of Emperor Alexander Severus at the hands of his own troops , initiating a fifty-year period in which 20 â `` 25 claimants to the title of Emperor , mostly prominent Roman Army generals , assumed imperial power over all or part of the Empire .
Simplified: The Crisis began with the assassination of Emperor Alexander Severus at the hands of his own troops in 235 AD . This started a fifty-year period in which 20 â `` 25 claimants to the title of Emperor , mostly prominent Roman Army generals , taking power over all or part of the Empire .