It is at least necessary to construct a constitution of equal power to the Articles of Confederation, which means a government that preserves the common peace, regulates commerce, and oversees relationships with foreign countries. Each job granted to the government should be granted along with the power to effectively carry out that job.
The national government is the logical choice to provide for common defense because it has the best understanding of the dangers that represents the whole nation so that it's concern extends to each part of the nation, and that has the ability to act uniformly.
The framers of the Articles of Confederation also believed that the unified government should provide for the common defense. However, the Confederation Congress failed to do so because it was given the responsibility of providing for the common defense without the power to do so. The unified government's only power existed through quotas and requisitions from the states. This failed because the responsibility was split from the power.
When the power to equip and fund a defense rests in the body that has the responsibility to do so, the responsible body will be able to provide for the common defense. There can be no restrictions placed upon a government's power to provide for common defense, as there is no way of knowing what kind of future threats may arise.
The threat to national security exists from Maine to Georgia, and an attack on the borders of one state is like an attack on all the states. If each state provided for its own defense, a state like New York will be burdened more than others. Furthermore, if an individual state does not provide adequate protection, then the entire nation is put in danger. If an individual state provides more than necessary and amasses more power than its neighbors, interstate tensions and jealousy could result in each state trying to out-do the others in military power. Competition could also arise between state military and national military.
The critics of the U.S. Constitution express concern about standing armies during times of peace. This should not be a concern because the legislature, as representatives of the people, are the ones to control the army and therefore cannot threaten the rights of the people without the people's approval. Furthermore, the clause that requires Congress to approve funding for only 2 years at a time will force the people, through their representatives, to vote frequently on the standing armies.