Even simple things about Sherry have been decided long ago. The capacity of the Sherry cask (butt) was set in the 1400s! To help Sherry stay stabilized during ocean voyages of these times, brandy was added to the wine. This is why Sherry is now a "fortified", or alcohol-added, wine.
In 1933 the Consejo Regulador was setup to protect Sherry's consistency. In the mid 1990s, the EU ruled that all EU nations must abide by the ruling that Sherry only comes from this region in Spain.
The three centers of Sherry in Spain are Jerez de la Frontera, Sanlucar de Barrameda, and Puerto de Santa Maria. Spain produces 19.8 million gallons of sherry a year. Other current producers of a "Sherry" are South Africa, Australia, France, and Germany.