By the eighth paragraph of Jonathan Swift's pamphlet titled A Modest Proposal, Swift identifies that "an American acquaintance in London" had assured the speaker that "a young healthy child well nursed, is, at a year old, a most delicious nourishing and wholesome food." Hence, the nationality of the friend who made the recommendation the speaker is basing his proposal on is American.
The reference to the American nationality is politically significant due to the fact that Swift was a Tory. Swift published his satirical pamphlet in 1729, a time when Ireland was experiencing what has been dubbed the Age of Ascendancy. Though Ireland was its own separate kingdom, it was controlled by England, and it was dominantly Catholic. England's break from the Catholic Church and creation of the Anglican Church posed significant hardships for dominantly Catholic Ireland. The Catholics of Ireland were no longer given the right to rule or vote. Instead, the few Anglican landowners in Ireland held all of the authority. What's more, most of Ireland's Catholic were poor commoners; hence, as the Anglican landed gentry ascended to positions of absolute authority, the impoverished Catholics became further oppressed. Swift strongly empathized with the suffering of the poor Irish Catholics even though he himself was Anglican and a Tory. The Tory party believed in absolute monarchism. Hence, while Swift saw a need to fix the impoverished conditions in Ireland, he also objected to any idea that Ireland break completely free from the King of England.
Meanwhile, American colonists were also beginning to show very anti-Tory sentiments. In 1729, England had recently finished defeating the French in the French Indian War, which secured Canada and other French territories for England but also left American colonists financially distressed because the war created wealth for the merchants but left the poor unemployed. On top of unemployment, England began taxing colonists more heavily in order to pay for the debts left by the war. Heavy taxation left American colonists wanting to be separated from the King of England, just like the impoverished Irish.
Hence, in referencing America, Swift is very cleverly satirizing anti-Tory sentiments, and since he was a devoted Tory, his satire is his way of denouncing anti-Tory sentiment even in the face of poverty and oppression.