One of the major reasons the back country settlers clashed with the established political authorities of the coast was

The answer that best completes the statement above is this: "the reluctance to spend tax money to protect settlers from Indian attacks." This is one of the main reasons why the back country settlers had a conflict with the established political authorities of the coast. One of the purpose of the tax money which are held by these authorities is for the protection of its citizens. But because they were just settlers, they did not provide protection for them against Indian attacks.