Answer:
establishing federalism.
Step-by-step explanation:
The purpose of the Tenth Amendment is to substantiate the interpretation, that the powers not surrendered to the central government of the United States, and at the same time not forbidden of the State, were fully given to the States or the people.
The above explanation corroborates with the concept of Federalism, which is based on the sharing of powers between the federal government and state governments, such that it allows each state to retain some sort of sovereignty (not entire sovereignty in Confederacy.)
Hence, it can be concluded that The Tenth Amendment was added to the Bill of Rights because the framers believed in the principle of establishing federalism.