You said human borders did not matter to God, I provided a scriptural reference of nations coming under severe judgment for altering borders. So, God does care about human borders.
A couple of notes about the Joel passage:
1) Do you think there was or will be a day when God gathers the nations for judgment?
2) The language of Joel is apocalyptic and not intended to be taken literally.
3) But if it is, the land that is divided is Israel and the nations that did the dividing are being judged by God for dividing...