It is a dispute over Justice. The land claim to Israel by two Judean tribes is unlawful. Scenario:
12 sons are given 12 houses in a trust fund. 2 of these brothers decide they don't like being out-voted by the other 10 who disagree with them in terms of how the trust is handled. So, the 2 sons hire a hit-man to kill their 10 brothers, and then apply to inherit their property.
If this case appeared before an American court, the 2 sons would not be allowed to inherit the land, life insurance or estate of their 10 other brothers. The 2 sons would go to jail for murder.
Now that's just the legal issue. Then there is the religious issue. According to the Torah, it is forbidden for one tribe to claim the inheritence (land or otherwise) of another tribe... tell me G-d, didn't see all this coming, lol. Technically, their state is unlawful in both legal and religious terms, so why should the Arabs honor or recognize it? Since when should criminal conduct become... legal?
Ninth Scribe