* Make it easier for everybody to make money. A unified America will be able to fend off competition from Europe, bargain from a stronger vantage point and -- very importantly -- be able to field a navy capable of protecting its commerce. Alexander Hamilton:
Under a vigorous national government, the natural strength and resources of the country, directed to a common interest, would baffle all the combinations of European jealousy to restrain our growth. This situation would even take away the motive to such combinations, by inducing an impracticability of success. An active commerce, an extensive navigation, and a flourishing marine would then be the offspring of moral and physical necessity. We might defy the little arts of the little politicians to control or vary the irresistible and unchangeable course of nature.
And, Hamilton adds, a bigger country means a more economically diverse country -- which will make it easier to ride out tough times in any particular industry.
* Make it easier to collect revenue to fund a national government. Remember, this is back before the IRS had really even been thought off, so many of the government's revenues came from import duties and that kind of thing.
* Get economies of scale. This idea might seem farcical at this point, now that the government is buried in debt, the idea was that one big government might be able to do things less expensively, on the whole, than if the 13 states were all spending money on their own and duplicating efforts. Some of that depends on the United States being a much smaller country; Hamilton at one point boasts that the Navy would only have to defend the country in the Atlantic. Projecting power around the globe wasn't really under consideration here.
But speaking of the rest of the globe, there's a kind of bizarre moment at the end of Federalist 11. Hamilton's been playing up the ability of the United States to make money and compete against Europe -- when all of the sudden he launches a sort of ur-Freedom Fries campaign.
Europe, by her arms and by her negotiations, by force and by fraud, has, in different degrees, extended her dominion over them all. Africa, Asia, and America, have successively felt her domination. The superiority she has long maintained has tempted her to plume herself as the Mistress of the World, and to consider the rest of mankind as created for her benefit. Men admired as profound philosophers have, in direct terms, attributed to her inhabitants a physical superiority, and have gravely asserted that all animals, and with them the human species, degenerate in America -- that even dogs cease to bark after having breathed awhile in our atmosphere.1 Facts have too long supported these arrogant pretensions of the Europeans. It belongs to us to vindicate the honor of the human race, and to teach that assuming brother, moderation. Union will enable us to do it. Disunion will will add another victim to his triumphs. Let Americans disdain to be the instruments of European greatness! Let the thirteen States, bound together in a strict and indissoluble Union, concur in erecting one great American system, superior to the control of all transatlantic force or influence, and able to dictate the terms of the connection between the old and the new world!
Which just goes to prove: There's no topic in American politics -- and never has been -- that can't be livened up with a little bit of good old-fashioned Euro-bashing. The French suck! USA! USA! USA!