In Gulliver's Travels, Swift manages to satirize politicians, religion, science, society, and even the king in 18th-century England, using the framework of what is, on one level, a child's fantasy tale, and on a deeper level, a very astute commentary on serious problems Swift saw in England.
During the first voyage, for example, while Dr. Gulliver is in the land of Lilliput, he discovers that the king chooses his ministers not on the basis of their political skills or desire to rule for the common good but on their ability to dance on a tightrope, a not-so implicit criticism of how King George's ministers obtain their positions. Swift also targets the prevailing political parties in England when he comments on the Lilliputians' religious divisions between those who wear low-heeled and high-heeled shoes and those how open their eggs from the small and large ends first, satirizing the relatively insignificant differences between the Low Church and High Church, and the constant struggle between the Catholics and Protestants.
When he gets to the land of the Brobdingnags, which has a peaceful society, Gulliver describes contemporary English politics and society to the king, whose response is that Gulliver's society must be filled with "the most pernicious Race of little odious Vermin. . . ." This is basically double-barreled satire: Swift's readers, who would have considered themselves to be the greatest of European socieites, are presented with a unflattering view of themselves from an ostensibly neutral observer, the King of Brobdingnag.
Swift's most culturally sensitive satire comes in the fourth voyage--the Land of the Houyhnhnms--where he meets a race of rational horses whose servants are basically non-rational human beings called the Yahoos, a word that has ever since been used to describe uncivilized, uncultured people. The difference between the rational horses and the Yahoos allows Swift to criticize the nature of man more closely than in the other voyages, and his view is that man, who should be controlled by the higher elements of his nature, is instead a victim of the baser elements.
All is not lost, however, because the aim of satire is to improve what is being satirized, and Swift has made a mighty attempt to improve his society.