The Articles of Confederation was the United States' first constitution. It was known for being very weak and giving little to no power to the federal government.
The Constitutional Convention of 1787 was originally called to revise and amend the Articles of Confederation. Many people were finally realizing that it was too weak and was hurting the country. One of the main weaknesses that the delegates at the Constitutional Convention saw was the fact that the federal government could not tax the states. In order for the government to get money, they had to outright ask the states for it. This was a huge problem, as this meant they could not pay for war debts or for other important matters.
The Articles of Confederation also contained many other weaknesses. The government could not draft soldiers, regulate trade, create and enforce laws properly, amend the Articles without the approval of the thirteen colonies, and as I said before, tax the states.
While the Constitutional Convention of 1787 was meant to simply amend the Articles of Confederation, that did not go as planned. They actually ended up getting rid of the Articles altogether, as they decided it was just a lost cause. They created the United States Constitution instead, which gave the government power.