There are a number of historical examples of confederacies that failed either due to infighting and competition amongst their members or invasion from outside forces. The Grecian republic ended in a series of restless alliances and usurpations that welcomed in Roman domination.
Germanic nations have attempted to sustain confederacies that result in wars amongst competing regions, the strong always preying on the week. And, the example of the United Netherlands provides evidence that a nation will disregard its constitution when need be to amass more power in unity than the confederacy can provide.
In the case of the first 6 years of the American confederacy, a number of very important deficiencies existed that could lead to a similar fate as these prior confederacies.
The Confederation Congress lacks sanction for any of its laws. There is no clause of mutual guarantee between states that would force a state to assist another state in repelling domestic dangers. Individual states can trample on the rights of citizens and the national government has no power to stop them.
The system of requisitions and quotas does not provide sufficient funds to the central government, and there is no effective and fair way to determine the worth of an individual state. This inequality of taxation could have destroyed the union long ago if there had been means of enforcement of collection as states that were unfairly taxed would most assuredly acted against the union on grounds of unfair treatment. The only sure way to sustain a flow of revenue for government is through direct taxes upon the citizens.
Congress cannot effectively regulate commerce. The inconsistencies that have resulted from states managing their own commercial policy have already damaged treaties with foreign nations.