Bill of Rights was added to Constitution to ensure ratification.
When the Convention reported the Constitution to the states for ratification, the nation split between Federalist supporters of the new document and Anti-Federalist opponents, who were especially concerned that it did not, like most state counterparts, have a bill of rights (of the 11 state constitutions in place in the years after independence, 7 had bills of rights). To ensure ratification of the document, the Federalists offered concessions, and the First Congress proposed a Bill of Rights as protection for those fearful of a strong national government. The Bill of Rights came into effect in December 1791, after ratification by three-fourths of the state legislatures.
