The primary purpose of the Articles of Confederation was to create a stronger, more unified nation in order to better protect and support individual states. It was a compromise between federalists and states' rights advocates, but in its final state, the document leaned heavily towards preserving state sovereignty. The federal government was allocated little power to enforce the laws the Articles of Confederation presumably hoped to apply.
There were numerous practical issues caused by the Articles of Confederation's failure to ensure federal power and unity. Meetings of the Confederation Congress were sparsely attended, often because members of individual states were more interested in maintaining their own stability than discussing national problems with other states. The Confederation Congress was run on a kind of honor system: all delegates and member states promised to rely on one another’s good judgment and mutual commitments to protect one another in times of war. There was no real way to ensure this promise was kept, however—another weakness of the document.
Also problematic was how to manage as-yet unclaimed territory. The northeastern region that would become Vermont was bickered over by New Hampshire, New York, and Massachusetts, each of whom wanted to claim it for their own. Meanwhile, the residents of the region itself petitioned to become an independent state.
The biggest problem with the Articles of Confederation was its weakness on financial matters. Without any power to tax, the federal government was essentially penniless and dependent on the states for funding—and few states were interested in parting with their own cash to support a unified government. When Congress attempted to pass tax acts that would help cover the costs of running a government, the states balked: it reminded them of unpopular British tax acts that helped prompt the Revolutionary War.
Ultimately, the Articles of Confederation failed to give Congress enough to power to ensure its aims were fulfilled. While state sovereignty would remain an important facet of American policy, the 1789 US Constitution vastly expanded the federal government's power, creating a stronger, more enforceable document.