What was the reason for telling the king about his invention?

Gulliver takes a sense of pride in his nation, and wants to impress the emperor, by telling him about his country's political system. Hence when expressing his nationalistic pride he mentions how gunpowder is perhaps one of the greatest inventions of mankind, and how it has safeguarded England's position as an unrivalled nation. He even offers to teach the emperor how to make gunpowder so that he could defeat all his enemies and reign supreme, an idea that the emperor rebuffs and is almost horrified by.