The Articles of Confederation is a document that gave power to the government while the individual states had little power.
The weakest part of the articles was the federal government's ability and power. This was a problem because the US was unable to pay debts after the war. The states were disunited on the decision of whether the articles were a good idea.
The Congress came together in Philidelphia in order to change the Articles of Confederation and fix all of its weaknesses. The federal power needed to be changed.