Question

What did anti federalists fear would happen if the constitution became law?

Answer 1

The Anti-Federalists feared that if the Constitution was ratified (became law) that it would give far too much power to the federal government over the states--leading to tyranny and the trampling of individual rights. 

Answer 2

Anti-Federalists were anti-federalists because they did not want a strong central government. This is why the Articles of the Confederation were approved before the Constitution.

The Articles states that the central government would be weak and the States would have the main power. This proved to be not a working system, because of this they created the Constitution, creating a strong Federal power.

This was the main fear of Anti-Federalists, they explained that they claimed independence from Britain because they did not a strong central government which could be tyrannic, and the federal government could lead this way.