Despite ruling a physically isolated kingdom that has no real need to be concerned with anyone else because it has no neighbors, the king of Brobdingnag is very interested to learn about the laws and culture of Gulliver's home. He is horrified when Gulliver begins to acquaint him with the customs of England, and he comes to believe that the British are selfish and warlike and dishonest "vermin." However, even beyond his disgust, the king develops a rather violent antipathy to both Gulliver and his countrymen when Gulliver tries to tell him about the wonderful virtues of an invention called gunpowder. Gulliver describes the great damage it can do in almost gleeful terms, speaking about men's limbs positively raining from the skies after their owners have been blown apart by gunpowder's awe-inspiring power. The king is less than impressed.
The king's response to Gulliver shows just how gentle and wise he is. Fundamentally benevolent, honest, and peace-loving, the king seems to assess the British in the way that Swift would like the reader to do; it's a rather harsh way to characterize the reality he wished to satirize, but satire is often caustic.