The Articles of Confederation was the first constitution for the United States, but was known for being very weak and giving little power to the federal government. Under the Articles of Confederation, the government could not tax the states, regulate trade, draft soldiers, or even create and enforce laws properly.
The government under the Articles of Confederation had little power and was essentially doomed to fail. One of the main problems was that the government had essentially no way to make money. Since the government could not tax the states or citizens, in order to make money they had to outright ask the states for it. As you can imagine, many of the states did not want to give up their money if they did not have to, so most of the time the government did not have money to pay for war items, soldiers, and other goods.
With the Articles of Confederation, they could barely raise an army or regulate trade, which hurt the country even more. Another huge problem was the problem of creating, amending, and enforcing laws. In order to pass a law, 9 out of 13 of the states had to agree to it, so it was very hard to pass anything.
During the Constitutional Convention of 1787, the original goal was to simply amend the Articles of Confederation, as it was not meeting the needs of the country. This did not go according to plan though, as the Articles of Confederation ended up getting scrapped and the United States Constitution was created in its place.
One key issue that arose during the Constitutional Convention was the balance of powers between the federal government and the state governments. Many people were still scared of the federal government obtaining power and wanted to keep most of the power in the hands of the state governments. This was solved with the separation of powers and checks and balances, which prevents the federal government from abusing its power.
Another key issue that arose during the Constitutional Convention was how representation in Congress was going to be counted. Small states wanted equal representation in Congress, while larger states wanted representation based on population. The Great Compromise settled this problem, which allowed for both representation based on population in the House of Representatives and equal representation in the Senate.