Federalist No. 19
In Federalist No. 19, Hamilton and Madison continue to address the ongoing issue of the insufficiency of the present confederation to preserve the union.
Analyzing the history of Germany, they note that if the nation happens, on any emergency, to be more united by the necessity of self-defense, its situation is still deplorable. This is because military preparations must be preceded by so many tedious discussions, arising from the jealousies, pride, separate views, and clashing pretensions of sovereign bodies, that before the diet can settle the arrangements, the enemy are in the field; and before the federal troops are ready to take it, are retiring into winter quarters.
Then, analyzing the history of Donawerth in Swabia, and a period in the thirty years' war in particular in which friction developed between the Lutheran majority and the Catholic minority when the Duke of Bavaria decided rest control from the Abb de St. Croix, they note that the city was in part of a feeble and precarious Union that we must avoid. The only reason the region did not fall into pieces entirely was that the members were week, and willing to accept the vast weight and influence of the emperor. But the reality was that it was a feeble and precarious Union with a repellant quality, incident to the nature of sovereignty that only served to prevent any reform whatever.
Furthermore, analyzing the Swiss cantons, which scarcely amount to a confederacy, which have no common treasury; no common troops even in war; no common coin; no common judicatory; nor any other common mark of sovereignty they find that they are kept together by the peculiarity of their topographical position; by their individual weakness and insignificancy; by the fear of powerful neighbours; by the few sources of contention among a people of such simple and homogeneous manners; by their joint interest in their dependent possessions ... and by the necessity of some regular and permanent provision for accommodating disputes among the cantons.. But if the dispute cannot be resolved by a tribunal of impartial parties, or one or more cantons do not adhere to the definitive sentence that the impartial tribunal devises, then under the treaty of 1683, the Duke of Savoy, can interpose as mediator in disputes between the cantons, and to employ force, if necessary, against the contumacious party. The lesson is clear - whatever efficacy the union may have had in ordinary cases, it appears that the moment a cause of difference sprang up, capable of trying its strength, it failed.
In other words, history has shown us again and again that weak confederacies don't last. A strong union is essential.