Who thought the constitution gave the federal government too much power

The Confederates (anti-Federalists)

Explanation:

Hence, they wrote the Confederate Constitution and would not accept the Federalist Constitution until the Bill of Rights was included

The Anti-Federalists had several complaints with the Constitution. One of their biggest was that the Constitution did not provide for a Bill of Rights protecting the people. They also thought the Constitution gave too much power to the federal government and too little to individual states. (found this on Google)