I'm just a dude interested in history, but i only used Wikipedia before discovering this sub and reading all the wonderful answers you have here. My question pertains to the events leading to the battle of Poltava between Sweden and Russia. Why would an army based so much on conserving their manpower and taking as few losses as possible like Sweden advance all the way to Ukraine (or Ruthenia) through "scorched earth"? And why Ukraine (or Ruthenia), and not Russia proper? Can someone explain the events leading up to the battle, and the thinking of Charles XII? (not necessarily the whole Great Northern War).
After charles XII defeated poland, russia had conquered Narva and started to build st peterburg. He had also built a number of forts to protect his new city. Charles couldn't storm these forts and didn't want to waste time on a long siege. So he decided to march on moscow instead. As you know the russians has scorched the earth and swedish army suffered a lot of atrition. He couldn't continue his march on Moscow and he coldn't go back because his army would starve or freeze to death. So he decided march south to Poltava and lay siege there. He hoped that this would lure the russian army down to Poltava and that the swedish army would win a dicisive battle once they attacked.