The biggest problems federal government's could face was that the federal government had no national military.
After the Revolutionary War, the so called "Continental army" was disbanded. If threaten by an external force, government was first needed to encourage citizens to join its lines in order to raise an army. Additionally, even though the Congress at the time had the power to determine how to fund and regulate a "Continental army", it had no power to compel states to respond requests for either troops or funding.
