Why was the Bill of Rights added to the Constitution after it was ratified?

Because its critics demanded one, and the price of ratification was a promise of amendments. The United States Bill of Rights is the first ten amendments to the Constitution, proposed after the often bitter 1787 to 1788 debate over ratification and written to address the objections raised by Anti-Federalists, who opposed the new frame of government. Several of them, such as Patrick Henry, Samuel Adams and Richard Henry Lee, were leading revolutionary figures. Elbridge Gerry's tract of objections, which went through 46 printings, particularly focused on the lack of a bill of rights.

Many critics were concerned that a strong national government was a threat to individual rights and that the President would become a king. In Massachusetts the impasse was resolved when Samuel Adams and John Hancock agreed to ratification on the condition that the convention also propose amendments. Thomas Jefferson, writing to Madison, put it this way: half a loaf is better than no bread.

The person who wrote the amendments had first opposed the idea. James Madison reasoned that a list of rights might imply that anything not on the list was not protected, and he and the other Framers believed natural rights were too numerous to list. But to secure ratification he agreed to support a bill of rights, and he even served as its author. He ran for Congress with a pledge to introduce one.

Congress approved twelve articles on 25 September 1789. Ten were ratified on 15 December 1791 and became the first ten amendments. They guarantee freedoms such as speech, publishing, religion and assembly. At first they applied only to the federal government, and their application to state governments began after the Fourteenth Amendment.