An industrialized country or place already has a lot of factories, mines, and machine-work. The -ed tells you the change has happened; it is a description of the result. News and geography use it all the time: industrialized nations, the industrialized world. British spelling: industrialised. Though actually, the line is messier than the tidy phrase. A place can have factories and still be called developing, and “industrialized” in headlines often just means “rich, with heavy industry.” Do not mix it with industrial: an industrial zone is a place for factories; an industrialized country is a country that has gone through that big shift. Industrialized is also the past of the verb: the coast was industrialized in twenty years.