Short answers, pulled from the story.
The word diplomacy emerged from the 18th-century French term diplomate, which itself derived from the ancient Greek diplōma. This Greek root roughly translates to an object folded in two and was used by ancient sovereigns to protect document privacy before envelopes existed.
Some of the earliest known diplomatic records are the Amarna letters written during the 14th century BC. These letters were exchanged between pharaohs of Egypt's eighteenth dynasty and rulers of Canaan called Amurru.
Milan became the first state to send a representative to France in 1455. Spain appointed an ambassador to England's Court of St. James's in 1487, marking the beginning of permanent missions across major European powers.
Diplomatic rights were formalized by the 1961 Vienna Convention on Diplomatic Relations which protects diplomats from persecution or prosecution. If a diplomat commits a serious crime while in a host country, they may be declared persona non grata and tried for the crime in their homeland rather than facing local courts.
China employs giant panda bears as diplomatic gifts known as panda diplomacy to build international partnerships. This form of soft power cultivates relationships respect or admiration from others to gain influence rather than using coercion.