Were the sackings a common strategy employed by the cities? Or were they uncommon and extraordinary events? Could you recommend any bibliography about the history of sacking?
Thank you very much in advance.
With regards to other Greek cities sacking was not that common and had significant psychological effects in the Greek world. We know that Alexander, prior to his conquest of the East, sacked the city state of Thebes which shocked the entire the Greek world due to its perceived brutality (our main source for this is diodorus). This is largely due to the Greeks having certain cultural customs in place that granted protection to other Greeks, for example it would be considered a great tragedy for a Greek to be enslaved by another Greek (something which the Spartans were criticised for doing).