Finally time for the last of the Bill of Rights, the 10th Amendment, as reproduced below.
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
This may be the last amendment in the Bill of rights, but it was probably the most important for preventing government over-reach. Stated another, potentially more clear way, any authority that the Constitution does not prohibit the States from exercising, and does not expressly grant as a power of the Federal Government, is the responsibility of the States, or the people.
This amendment to the Constitution should nullify a significant portion of the powers the Federal Government has claimed for itself over the years. Those areas that the Federal Government exercises power over, that are not expressly identified in the Constitution as one of its powers, it has no authority in.
For example, the Constitution does not mention education, so the Federal Government has no authority in the realm of education. The Department of Education is an unconstitutional body. The Constitution also does not mention agriculture, so the Department of Agriculture is an unconstitutional body. This list of unconstitutional agencies goes on and on: the Federal Drug Administration, the Environmental Protection Agency, the Drug Enforcement Agency, etc., etc.
The 10th Amendment also gives the States the ability to refuse to aid the Federal Government in enforcing laws and regulations over which is has no authority, or even outright prevent their enforcement within their borders. This is another important factor in preventing government over-reach. Without the cooperation of the States, the Federal Government does not have the resources and man power to enforce all the additional powers it has tried to grant itself.
The Federal Government was intended as a way for States to solve disputes between them, and as a convenience for defending themselves and dealing with other nations. It was never meant to exercise any additional authority over them. This amendment was meant as a way of preventing that consolidation and growth of power.