Why is diplomacy a key part of U. S. foreign policy?

The US is one of the most developed countries in the world and as such has one of the strongest militaries. Because of that, it has often been the leader establishing world peace and initiating missions with the United Nations aimed at bringing democracy and liberty to various places around the globe. It has negotiated peace treaties between many warring sides, and since everyone wants its support, it has always had to have good diplomats worldwide.