Final answer:
The Constitutional Convention of 1787 was called because the Articles of Confederation were ineffective, leading to the creation of the U.S. Constitution with a stronger federal structure.
Step-by-step explanation:
The Constitutional Convention of 1787 was called primarily because C) The Articles of Confederation were seen as ineffective. The economic crisis of the 1780s, deficiencies in the Articles, and challenges like Shays' Rebellion highlighted the need for a more robust federal structure. As delegates convened in Philadelphia, they shifted their mission from amending the Articles to creating a new framework for a national government. This framework was the United States Constitution, which provided a balanced distribution of power between the national government and the states, while also expanding the powers of the central government.