In the late 1780's, states were debating whether or not to ratify the Constitution. They were broken into two different state convention groups, those who were for and those who against ratification: the Federalists and the Antifederalists.
Federalists were in favor of a strong government and wanted the constitution passed as it was. The Antifederalists formed as opponents to the Federalists. They thought that the Constitution gave the central government too much power, and left the states with with not enough.
State constitutions usually included a bill of rights, which was missing from the Constitution of the United States. This was the main reason why certain states who were not in favor of ratification.
Eventually, the Federalists promised to add a bill of rights, after ratification. This was the main factor that encouraged many states to vote for ratification in the end.
