The French believed the Ohio River was their territory because back when England and France and Spain owned most of North America, The French and English were fairly close to the Ohio River.
So therefore, since the French was fairly close to the Ohio River, which was “technically” owned by the most of the English, they thought they owned most or all of The Ohio River.
I might be wrong, so I’d recommend to be wary (careful) on this question and my answer.
