I once asked my dad why people who committed treason against the king in medieval times were treated so cruelly.

He said that live was nasty, brutish and short in those days, and to make an impact and a deterrence the king had to be over the top cruel.

I don't know how true that is, as I suspect there's a large element of people just liking to be cruel if they have the opportunity.

I have a couple books on the cruelties done by armies in WW2, and in the American west, and could not finish reading them.