Original: Henry quickly gained enough power and support to have himself declared King Henry IV, to imprison King Richard, who died in prison under mysterious circumstances, and to bypass Richard's seven-year-old heir-presumptive, Edmund de Mortimer.
Simplified: Henry gained enough power and support to have himself declared King Henry IV. He imprisoned King Richard (who mysteriously died in prison) and by-passing Richard’s seven-year-old heir presumptive Edmund de Mortimer.