the "storia d'italia" by guicciardini is the best work by a contemporary about the first half of the XVI century, a fascinating book in my opinion. I dont't know where you are from so maybe you don't know that the opera of guicciardini is important above all because it influenced modern italian language. in this context its importance is comparable to dante's divina commedia for example. that book is maybe one of the best witnesses of the wars of italy, at least as far as I know. if you post this also in r/italy I'm sure you'll be given more exhaustive information.