Why did the U. S. feel it had to write another Constitution?

Basically, the Founding Fathers wanted a new constitution because the government under the Articles of Confederation proved to be unstable and inefficient.

Explanation:

The document provided very little structure in terms of a federal government. Each state used their own currency and there was little unity. Finally, with Shay's rebellion in Massachusetts and no standing army to counteract it, the Founding Fathers came to the conclusion that a new government and constitution needed to be drawn up which would give America a stronger federal government while still preserving state's rights. More input from FAQ Farmers: * The Founding Fathers wanted a new constitution because the current government of the Articles of Confederation was not working due to the balance of powers between state and federal governments. The document gave state governments too much power and left the federal government helpless in both defending and caring for American interests. This eventually led to almost no unification of the states. Two parties emerged. The federalists, who lobbied for a strong central government, and the anti-federalists who emphasized state and individual rights. The two parties compromised and worked together to ratify the new Constitution that granted more power to a federal government and granted less power (but still protected) to the states. * After the Shay's Rebellion, the Founding Fathers realized how weak the Articles of Confederation was. The federal government was powerless to stop the rebellion and Congress had little power. Some weaknesses of the Articles of Confederation included that was no chief executive, Congress had no power to tax citizens directly, no power to draft an army, had no national court system, no power to settle arguments among states, and many more. This led to the Constitutional Convention (started by Alex Hamilton), where the AoC was scrapped and a new constitution was written.