Federalist #9,
and especially #10, "Union as a Safeguard Against Domestic Faction and Insurrection" are recognized as two of the most important philosophical of the Federalist papers.
Federalist # 9 Publius. [Alexander Hamilton] 
A firm Union will be of the utmost moment to the peace and liberty of the States, as a barrier against domestic faction and insurrection. It is impossible to read the history of the petty republics of Greece and Italy without feeling sensations of horror and disgust at the distractions with which they were continually agitated, and at the rapid succession of revolutions by which they were kept in a state of perpetual vibration between the extremes of tyranny and anarchy. If they exhibit occasional calms, these only serve as short-lived contrast to the furious storms that are to succeed. If now and then intervals of felicity open to view, we behold them with a mixture of regret, arising from the reflection that the pleasing scenes before us are soon to be overwhelmed by the tempestuous waves of sedition and party rage. If momentary rays of glory break forth from the gloom, while they dazzle us with a transient and fleeting brilliancy, they at the same time admonish us to lament that the vices of government should pervert the direction and tarnish the lustre of those bright talents and exalted endowments for which the favored soils that produced them have been so justly celebrated.
Full Document
Federalist #10
Publius. [James Madison] 
Among the numerous advantages promised by a well constructed Union, none deserves to be more accurately developed than its tendency to break and control the violence of faction. The friend of popular governments never finds himself so much alarmed for their character and fate, as when he contemplates their propensity to this dangerous vice. He will not fail, therefore, to set a due value on any plan which, without violating the principles to which he is attached, provides a proper cure for it. The instability, injustice, and confusion introduced into the public councils, have, in truth, been the mortal diseases under which popular governments have everywhere perished; as they continue to be the favorite and fruitful topics from which the adversaries to liberty derive their most specious declamations. The valuable improvements made by the American constitutions on the popular models, both ancient and modern, cannot certainly be too much admired; but it would be an unwarrantable partiality, to contend that they have as effectually obviated the danger on this side, as was wished and expected. Complaints are everywhere heard from our most considerate and virtuous citizens, equally the friends of public and private faith, and of public and personal liberty, that our governments are too unstable, that the public good is disregarded in the conflicts of rival parties, and that measures are too often decided, not according to the rules of justice and the rights of the minor party, but by the superior force of an interested and overbearing majority. However anxiously we may wish that these complaints had no foundation, the evidence, of known facts will not permit us to deny that they are in some degree true. It will be found, indeed, on a candid review of our situation, that some of the distresses under which we labor have been erroneously charged on the operation of our governments; but it will be found, at the same time, that other causes will not alone account for many of our heaviest misfortunes; and, particularly, for that prevailing and increasing distrust of public engagements, and alarm for private rights, which are echoed from one end of the continent to the other. These must be chiefly, if not wholly, effects of the unsteadiness and injustice with which a factious spirit has tainted our public administrations.
Full Text of Federalist #10
