Complex sentence: It is a chronicle of English history from the earliest times to about the year 1362, however its main value is for the reigns of Edward I and Edward II and part of that of Edward III when Grey was alive.
Split into simpler sentences: It is a chronicle of English history from the earliest times to about the year 1362. However its main value is for the reigns of Edward I and Edward II and part of that of Edward III when Grey was alive.