According to David Reynolds the word Summit began being applied to diplomacy and international politics in 1950 when Winston Churchill first called for “another talk with the Soviet Union at the highest level… a parley at the summit”. The use of the word “summit” then probably stuck once expeditions to the world’s highest peak became important events. Indeed, in 1953, Edmund Hillary and Tenzing Norgay became the first men to reach the summit of the Everest; the same year that Mr. Churchill repeated his appeal for peace “at the summit of the nations”.
This may then explain why Churchill´s metaphor stuck and why today the word is used to characterize high-level meetings between state representatives.
In his book, David Reynolds also shows some interesting depictions at the time of cartoonists who portrayed world leaders on the top of mountains. Henceforth, newspapers also began applying the term, which nowadays is of common usage around the world.
Reynolds, David. Summits- Six Meetings that Shaped the Twentieth Century, Penguin Books. London, 2008.
The New York times PAGE ONE 100 Years of Headlines. New York, 2000