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, draft soldiers, regulate trade, or create and enforce laws properly.
Since the federal government could not tax the states under the Articles of Confederation, it made it difficult for them to be able to obtain money to pay for war, soldiers, or other expenses. The only way they could obtain money was by outright asking the states to give them money. Obviously, this did not go well, as a lot of the states did not want to give up money if they did not have to. While obtaining loans from other countries was an option too, a lot of foreign countries were hesitant, as they believed that the United States would not be able to repay them.
During the Constitutional Convention of 1787, the original goal was just to amend the Articles of Confederation. This did not happen though, as the Articles of Confederation ended up getting scrapped altogether and the United States Constitution was created instead. With the United States Constitution, the government could tax the states and obtain money for important expenses.