When the United States gained independence from Britain, they needed to establish a new government as well as rules for that government. Since they had just fought a difficult war, which was still fresh in the minds of the newly independent Americans, they were very careful in how they designed the government. They did not want to have fought a war for independence from a government that abused its power only to institute a new government that did the same. This fear of a strong federal government led to the creation of the Articles of Confederation.
Due to their fear of a government with too much power, the Articles of Confederation were purposely designed to create a federal government with very limited power. Instead, more power was given at the state and local levels of government. The problem, however, was that the federal government didn't have enough power to carry out any duties. As the other educator pointed out, the weaknesses were numerous and were quickly highlighted through events like Shays' Rebellion.
The Constitution was designed to fix many of the problems that existed with the Articles of Confederation; however, all Americans were still not fully in support of it. Anti-Federalists felt it was an overreaction and that it provided the federal government with too much power. They were afraid that a government with too much power would lead to the loss of rights of American citizens. Eventually, an agreement was reached between Federalists and anti-Federalists. The agreement involved ratifying of the Constitution as the new governing document of the United States, but only with the addition of the Bill of Rights, which sought to guarantee and protect certain rights for Americans.