What was the Constitutional Convention originally called to do? What happened instead?

The initial aim of the Convention was only to reform the so-called Articles of Confederation, the first U. S. government document, in force since 1781 and which was clearly proving insufficient to respond to all the problems arising after Independence. Thus, by September 1786, commissioners from five states had met at the Annapolis Convention to discuss such reforms, and shortly thereafter invited representatives of the remaining states to join the federal government's plan for improvement.

Explanation:

to solve the problems of government of the United States of America, the government of which was defined according to the Articles of the Confederation after its independence of Great Britain.

As a result, the only and current constitution of the United States, which created the United States federation with its present structure, was enacted, and therefore the convention is one of the most important historical events in the history of the United States.