To pillage is a term of war that means to take everything of value from a place that you've conquered, but these days, pillage can be used to talk about anyone who takes what's not theirs.
It wasn't enough just to win a battle. A conquering army had to pillage entire cities, taking everything of value that wasn't nailed down. Recently, several European families have won cases in international courts against museums displaying art that was looted by the Nazis during World War II. These families claim that the art was pillaged during the war and that, rather than being displayed on museum walls, it should be returned to its rightful owners.