What was one of the reasons the anti-federalists were opposed to the constitution?

They afraid central government to overpower state government.

Explanation:

The Anti-federalist argued that a strong central government would make the state government become irrelevant, or losing state autonomy.

They also use Article 1 Section 8 Elastic Clause which provide Congress the power " to make any law that necessary and proper" to against ratification because it give an indefinite power to the federal government.

first representative government in british america called virginia assembly