In fact, in the pre-modern world there were large spans of space and time where growth was so slow as to be invisible within a person's lifetime and people did

In fact, in the pre-modern world there were large spans of space and time where growth was so slow as to be invisible within a person's lifetime and people did think of wealth as being zero-sum. To a feudal lord, land = wealth and being wealthier was about having more land. Someone already had all the land, so the only way of getting more was taking someone else's.