What are three reasons that the constitutional convention decided they needed a document to me the articles of confederation

Any of these should suffice.

1. The states didn’t act immediately. It took until February 1779 for 12 states to approve the document. Maryland held out until March 1781, after it settled a land argument with Virginia.

2. The central government was designed to be very, very weak. The Articles established “the United States of America” as a perpetual union formed to defend the states as a group, but it provided few central powers beyond that. But it didn’t have an executive official or judicial branch.

3. The Articles Congress only had one chamber and each state had one vote. This reinforced the power of the states to operate independently from the central government, even when that wasn’t in the nation’s best interests.

4. Congress needed 9 of 13 states to pass any laws. Requiring this high supermajority made it very difficult to pass any legislation that would affect all 13 states.

5. The document was practically impossible to amend. The Articles required unanimous consent to any amendment, so all 13 states would need to agree on a change. Given the rivalries between the states, that rule made the Articles impossible to adapt after the war ended with Britain in 1783.

6. The central government couldn’t collect taxes to fund its operations. The Confederation relied on the voluntary efforts of the states to send tax money to the central government. Lacking funds, the central government couldn’t maintain an effective military or back its own paper currency.

7. States were able to conduct their own foreign policies. Technically, that role fell to the central government, but the Confederation government didn’t have the physical ability to enforce that power, since it lacked domestic and international powers and standing.

8. States had their own money systems. There wasn’t a common currency in the Confederation era. The central government and the states each had separate money, which made trade between the states, and other countries, extremely difficult.

9. The Confederation government couldn’t help settle Revolutionary War-era debts. The central government and the states owed huge debts to European countries and investors. Without the power to tax, and with no power to make trade between the states and other countries viable, the United States was in an economic mess by 1787.

10. Shays’ rebellion – the final straw. A tax protest by western Massachusetts farmers in 1786 and 1787 showed the central government couldn’t put down an internal rebellion. It had to rely on a state militia sponsored by private Boston business people. With no money, the central government couldn't act to protect the "perpetual union."

he will find out what went wrong or happened and how.