The event preceding the Constitutional Convention that gave a legal foundation to the Convention was the Annapolis Convention of 1786 (also known as the Meeting of Commissioners to Remedy Defects of the Federal Government).
The Annapolis Convention was held to discuss the problems that were hindering interstate trade. There were only twelve delegates representing five states at the convention. The Annapolis Convention found that the Articles of Confederation caused interstate commerce issues, as well as deeper issues due to a weak federal government. These findings eventually led to the Constitutional Convention wherein the Articles were replaced with the Constitution.