The question as worded is ambiguous since Palestine refers to several different things.
1) Land: The lands commonly referred to by the term "the Mandate of Palestine" came into existence (according to science) hundreds of millions of years (if not billions of years ago) from interactions between the African and Arabian Plates.
2) Mandate of Palestine: The British Mandate of Palestine was created during the Treaty of Versailles negotiations when the British Ambassador drew a line on a map and called it Palestine in 1919. In 1922, the area currently known as Jordan was separated jursidictionally from the Mandate of Palestine, giving the Mandate its present shape.
3) Current Nation of Palestine: The Nation of Palestine was created by the Oslo Accords in 1993. This document created the Palestinian Authority which became the recognized government of the State of Palestine. Palestine has embassies in numerous countries (except most Western States) as a result. (There are also embassies from before this point in countries that did not recognize Israel before the 1960s, but they were more symbolic than representative of an actual governing agency.)
The Airs of Palestine was created in 1816.
Palestine Railways was created in 1920.
Palestine Times was created in 2006.
Palestine pound was created in 1927.
Palestine Exchange was created in 1995.
Underground to Palestine was created in 1946.
Students for Palestine was created in 2009.
Palestine Lodge was created in 1926.
ArtSchool Palestine was created in 2005.
Palestine Association was created in 1805.
Palestine Regiment was created in 1942.
Palestine - comics - was created in 1996.