One of the provisions of the Treaty of Versailles ending WWI was that only France could sell the bubbly as ‘champagne’. Since the United States never ratified the treaty ‘champagne’ can be sold from California or anywhere else in the United States.
(Great Courses – World War I)
I know even now some food shows (although probably earlier reruns) still say that the label ‘Champagne” can only be used on bubbly from France.