Final answer:
Antifederalists feared the Constitution gave excessive power to the national government and weakened state governments, leading to their insistence on a Bill of Rights for individual liberties.
Step-by-step explanation:
The Antifederalists were proponents of strong state governments and opposed the new U.S. Constitution because they feared it created too powerful a national government and a too weak state government system. They believed that the Legislative Branch was given too much power without sufficient checks, and were concerned about the Executive Branch, particularly the unchecked power of the President. Ultimately, they pushed for the addition of a Bill of Rights to the Constitution as a safeguard to ensure individual liberties were protected against potential tyranny.