A major failing of the United States Government under the Articles of Confederation was its

lack of flexibility really

Explanation:

It's was either everyone agreed or nothing changed at all. So if they needed to make a change in their laws, the issue had to be highly sought after or effect many to the point that all the members saw how large the problem was. Because if you think about it, it wasn't easy to get a large group of very opinionated people to go to one side on a subject that could untimely have an unknown effect on the developing country.  

Anti-federalists were concerned that the constitution did not equally divide power amount the three branches of government. They also worried about giving the federal government the power to regulate commerce.