The word 'diplomacy' comes from a Greek term for a folded document
Before envelopes existed, rulers granting a privilege folded the document in two to keep its contents private. The ancient Greek diplōma, something doubled over, gave eighteenth-century French the word diplomate, and the name of an official paper slowly became the name for the whole art of dealing between states.
Diplomacy is communication by representatives of states and other institutions aimed at shaping international events, and it is the main tool of foreign policy. Treaties, alliances and agreements usually grow out of it. Modern methods derive largely from seventeenth-century European custom, the profession took shape in the early twentieth century, and a 1961 treaty agreed in Vienna, accepted by most of the world's states, now sets the rules for envoys, ambassadors and the embassies and consulates they staff.
The practice is far older than its name. Around 2100 BC the Mesopotamian city-states of Lagash and Umma concluded peace treaties, and in the fourteenth century BC Egyptian pharaohs corresponded with rulers in Canaan in what are called the Amarna letters. After the Battle of Kadesh in 1274 BC, Egypt and the Hittite Empire agreed one of the first known international peace treaties, fragments of which survive on stone tablets. Greek city-states sent envoys for particular negotiations but kept no permanent ambassadors; instead a proxenos, a local citizen friendly to another city, looked after its interests.
China developed a rich tradition during its era of warring states, when the persuader-diplomat became an idealised figure and Sun Tzu, author of The Art of War, emerged as one of the first realist thinkers. The Han dynasty, unable to defeat the nomadic Xiongnu, paid them tribute and sealed a marriage alliance, and a treaty drafted in 162 BC assigned everything north of the Great Wall to the nomads and everything south to the Han. Japanese missions travelled often to Tang China until 894, when that dynasty seemed close to collapse.
Renaissance Italy helped shape the modern diplomat. Genoa and Venice came to rely less on naval strength than on good relations with the Ottoman government, known as the Sublime Porte, and exchanges among merchants, envoys and clergy produced new forms of statecraft. Gradually the diplomat changed from a negotiator sent for a single task into a standing representative of an independent state.
Source: Diplomacy
