Articles of Confederation
The Articles of Confederation empowered the states to govern as they pleased and be separate from one another.
The central government had no power to tax or enforce laws. It was an arbitrary "union" of the states that only worked successfully to unify the people during wartime.
The central government was weak because the states did not identify with one another as one nation. They were each their own independent colony with their own distinct ideals. The Anglican aristocrats of Virginia did not identify with the Congregationalists in Massachusetts. The Quakers of Pennsylvania did not identify with slave owning plantation owners of the Deep South. They were all different from each other and did not necessarily want to be one united nation. Independence was the common goal, not a powerful union.