One aspect of Swift's style is to make Gulliver (and by extension, Swift's contemporaries) appear ludicrous through trying to explain human institutions to the various peoples he encounters. His attempts to describe the various causes of European wars to the leader of the peaceful Houyhnhnms, is a particularly relevant example:
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether the juice of a certain berry be blood or wine; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire...Sometimes the quarrel between two Princes is to decide which of them shall dispossess a third of his dominions, where neither of them pretends to any right. Sometimes one Prince quarreleth with another, for fear the other should quarrel with him
European customs and mores make no sense to many of the peoples Gulliver encounters, and of course Swift's point is that we ought perhaps to to reconsider some of them. Swift also wrote his story at a time when travelogues of foreign, exotic lands were very much in vogue for European readers just becoming conscious of a much larger world. Swift was thus able to play on an emerging sense of relativism among some European intellectuals, as well as appeal to a common trope in contemporary literature.
Gulliver also encounters utopias, or near utopias, such as those of the Brobdingnagians (and, for that matter, the Houyhnhnms.) But in each case, he raises important question as to whether these sorts of societies are obtainable for human beings. By portraying the Houyhnhnms, in particular, as horse-like beasts, he seems to be suggesting that human passions would make the kind of peaceful society they live in impossible.
Swift also uses characters to allegorically represent some figures that would have been recognizable to his readers. Lilliput is England, while Blefuscu is France. Their ceaseless conflict is based on the most foolish of reasons, namely that some in Blefescu interfere in the Lilliputian controversy over whether to break an egg at the big end or the little end. This, of course, is a satire of the Stuarts' associations with France. Swift thus savagely mocks political issues that had led to constant warfare in the early eighteenth century.