What were the causes of unrest in the American backcountry in the mid-eighteenth century?have support details.

The majority of the French and Indian War from 1754 - 63
was fought on the frontier--the edge of settlements in the Appalachian Mountains--so
part of the unrest and discontent was caused by the direct threat during that conflict
and how vulnerable those settlements were.

But I would say
that most of the tension and unrest came from long-running conflicts with Native
American tribes, and tension between settlers and the policies of England and the King. 
Most of those who lived on the frontier were Scotch-Irish, who held no love for the King
as it was.  They viewed restrictions on where they could settle or taxes they were asked
to pay as just a continuation of what they had endured back in
Ireland.