As F. P. Lock observes,
Swift's original impulse in writing Gulliver's Travels was certainly to create a general satire on the follies of European civilization as a whole. . . . (F. P. Lock, The Politics of Gulliver's Travels. Oxford: Oxford University Press, 1980. p. 69)
In Part I, Swift uses the Emperor of Lilliput, whose mind is as limited as his body is small, to satirize the greed, corruption, and war-mongering of England's King George I and Queen Anne. In Part II, the satire rests on the contrast between the Brobdingnagian king, who is the essence of a benign and moral leader, and George I, who looks even worse by this contrast than the Emperor of Lilliput. Perhaps Swift's most biting element of satire in Part II lies in the interchange between Gulliver and the king about the use of gunpowder and cannons as a tool of political power.
Gulliver introduces the King to one of the most powerful tools of warfare, which has the additional benefit of enabling a king to control his own people:
I told him of an invention, discovered between three and four hundred years ago, to make a certain powder, into a heap of which, the smallest spark of fire falling, would kindle the whole in a moment, although it were as big as a mountain, and make it all fly up in the air together, with a noise and agitation greater than thunder.
As one would expect from a morally just leader, the King is not horrified by the concept of such a weapon but is also surprised that such small creatures (Europeans) would harbor such horrendous thoughts, especially without any apparent thoughts of remorse about the terror and bloodshed of such weapons. He is, in short, utterly mystified that Gulliver's fellow Europeans could regard such destructive power without any moral reservations.
Gulliver's astonishment highlights Swift's condemnation of European savagery and its callous disregard of human rights:
A strange effect of narrow principles and views! that a prince . . . of strong parts, great wisdom, and profound learning . . . should, from a nice, unnecessary scruple, whereof in Europe we can have no conception, let slip an opportunity put into his hands that would have made him absolute master of the lives, the liberties, and the fortunes of his people!
By setting up the King of Brobdingnag as the fool who fails to recognize the powerful tool Gulliver is willing to put into his hands, Swift creates the dramatic contrast between the just ruler of this exotic land and the current King of England who, by implication, would embrace such a weapon in a heartbeat. To characterize the Brobdingnagian response as the "effect of narrow principles and view" points up the perversity of Gulliver's and, by reference, the European attitude toward such power.
Swift, through the voice of Gulliver, then, has managed to condemn the European ruler's lust for power and acceptance of mass destruction by merely creating its opposite, a humane, morally just leader who is shocked that anyone could think the destructive power represented by gunpowder could possibly be a beneficial thing.