Maybe it means that there’s a difference between how much land they own or something. It says there was a difference between the amount of land they occupied and the amount of land they couldn’t control. So maybe they didn’t own/have a lot of land but there was a lot of land they couldn’t get to/take over etc. or maybe this situation could be vice versa so they have a ton of land but only a little isn’t “controlled” let me know if this helps sorry if it’s confusing I’m just guessing based on the context clues :)
