Federalist Paper #20 is a continuation of The Insufficiency of the Present Confederation to Preserve the Union, Alexander Hamilton and James Madison bring to a conclusion the extended argument, begun in Essay #15, that the Articles of Confederation do not afford enough power and authority to the national government.
The system of government provided for in the Articles ultimately amounted to collection of independent, sovereign states, loosely united under a weak central government where the central government was unable to impose laws directly on the citizens and could only require action from the states.
As a result, this paper argues, violence and the “coercion of the sword” would inevitably replace law and “coercion of the magistracy.” In a system composed of multiple sovereigns, the only way to compel one of those entities to act would be through violence. Since the national government could not bring a state to court as with an individual, the stage could lead to instability, division and civil war.
Madison and Hamilton are calling for is a system that allows the national government to create laws that are directly applicable to individual citizens.
The national government must have supreme authority, they argue. Otherwise, disunion and even anarchy will result from multiple sovereigns (i.e. the thirteen states) competing with one another for supremacy.