Why were the Articles of Confederation a failure, and how did the Constitutional Convention address the problems under the Articles?
The Articles of Confederation failed because they did not give Congress and the national government enough power. The new United States just fought a war to end what they considered tyrannical rule of a strong government that overpowered local government and the leaders of the U.S. feared a powerful central government. Because of this, they did not give the central government the power it needed to rule effectively. It did not give Congress the power to tax, so the government ended up printing money which caused inflation. It did not give Congress the power to draft troops, so the U.S. military was small leaving the U.S. weak. Congress did not have the power to control interstate commerce or stop states from printing their own money, causing economic chaos within the U.S. The Articles did not give Congress the power to place tariffs on foreign goods, hurting American businesses that could not compete with cheaper British goods. The U.S. government had no chief executive so there was no one to enforce the laws that were passed. The list can go on. With the rebellion led by Daniel Shays in Massachusetts, the leaders of the U.S. realized the Articles were not working which led to the Constitutional Convention where the Articles were abandoned and the new U.S. Constitution was written.
The Constitution addressed many of the problems created by the Articles by creating a federal system of government with a much more powerful national government. It gave the national government the power to tax, draft troops, control interstate commerce, etc. It also created an executive branch and a federal court system, both of which were lacking under the Articles of Confederation. The greatest argument against the new Constitution was that it gave the national government too much power. This argument was addressed by the framers by creating a system of checks and balances, creating a system with three branches, each with its own separate powers (separation of powers), and creating a federal system where powers were divided between the federal government and state governments, with some powers delegated to the federal government, some reserved to the states and some shared by both.
The politicians responsible for framing the Constitution argued that the Articles of Confederation failed, essentially, because of the lack of a strong central government. The unicameral legislature under the Articles had no power to tax, no ability to regulate interstate commerce, and structurally was set up so as to be difficult to amend. The Constitution addressed these deficiencies by establishing a system of federalism in which the federal government was supreme. They gave Congress the power to tax and to regulate interstate commerce. They also created a strong executive, which the government under the Articles lacked. While many, described by their opponents as "anti-Federalists," thought the delegates to the Constitutional Convention had overcorrected, giving too much power to the central government, I'd argue that the Constitution is perhaps best understood historically by thinking of the problems under the Articles that it was designed to address.
Here is a video about the Articles of Confederation: