I have to write an essay comparing the Articles of Confederation and the Constitution at the time prior to ratification of the Constitution. Compare and contrast them by looking at three major points between the two.

Here are three useful points of comparison between the Articles of Confederation and the Constitution that you might like to consider:
1. The role of central government. The attitude toward central government displayed in the Articles was a holdover from the American colonists' war with the British. The colonists believed they were fighting against a tyrannical central government that was attacking Americans' fundamental rights and liberties. So when they established the Articles of Confederation, the colonists deliberately made sure that the central government was weak, and that ultimate sovereignty would lie with the states.
However, this created problems of its own. Without a strong central government, the United States was unable to pay its debts, develop a coherent foreign policy, or handle domestic disturbances. The Constitution, then, established a relatively strong federal government that could handle these problems while at the same time still granting to the states a fair degree of power in the new system.
2. The role of the states. This point is closely related to the first. The Articles of Confederation were based on a philosophy of radical republicanism, so eloquently expressed by Thomas Jefferson in the Declaration of Independence. The states were held to be sovereign under the Articles, which established a very loose arrangement between them. It was believed that a confederation would ensure that the states retained their sovereignty while at the same time being able to work together to solve common problems that all Americans faced.
As we've already seen, however, the system wasn't very effective in dealing with outbreaks of lawlessness and civil disturbance. Too much depended on the willingness of each individual state to act. If they couldn't or wouldn't act to stamp out disturbances, there was little that Congress could do to prevent rebellion from spreading across state lines. Indeed, it was one such rebellion—Shay's Rebellion—that led directly to the convening of the Constitutional Convention. The new Constitution ensured that a strong federal government would have the power to quell outbreaks of disorder that threatened the stability of the United States as a whole.
3. The institution of the Presidency. Under the Articles of Confederation, the United States didn't have a President. The American colonists didn't want a strong executive; it smacked too much of King George III. Americans had just fought a war against a king, and the last thing they wanted was to see another one established on American soil after all that blood and sacrifice.
But once it was established that the United States needed a strong central government, thoughts inevitably turned to setting up an executive branch, and that's precisely what the Constitution did. Even so, the powers of the president were circumscribed, in keeping with the Framers' inherent distrust of placing too much authority in the hands of one man. For instance, Article II of the Constitution stipulates that the president cannot declare war; it also prohibits his involvement in the regulation of commerce. Instead, these powers were vested in the United States Congress.