Final answer:
The Anti-Federalists are the group that argued the national government would be too powerful under the new Constitution and would usurp important powers from the states and their people.
Step-by-step explanation:
The group that would have made the argument that "The national government under the new Constitution will be too powerful and will take important powers away from the states and their people" during the debate over ratification of the Constitution were the Anti-Federalists. The Anti-Federalists were concerned that the new Constitution granted the national government too much power and lacked a bill of rights to protect individual liberties, a view that was in opposition to the Federalists who supported a stronger national government and later promised the creation of a Bill of Rights. Notable Anti-Federalist figures included Patrick Henry and George Mason, who feared that the new Constitution would lead to a loss of state sovereignty and the formation of a political aristocracy.