"If every present-day territorial claim depended solely on identifying the earliest inhabitants..."

Example:

Suppose archaeological evidence shows:

• Group A lived in an area 6,000 years ago.
• Group B arrived 4,000 years ago.
• Group C arrived 2,000 years ago.
• Group D lives there today.

If the legal rule were simply:

"The earliest inhabitants always have the strongest claim,"

questions immediately arise:

• What if the descendants of Group A no longer exist as a distinct community?
• What if the evidence is incomplete or disputed?
• What if populations mixed over millennia?
• What if multiple migrations occurred?

The further back historians go, the more fragmentary the evidence often becomes. That makes applying a simple "earliest occupant" rule increasingly difficult.