Why did Argentina and Brazil not dispose of their older dreadnoughts in the 1920s?
Short answerThey were obsolete against the largest world navies but still useful against each country's principal regional rival.
NotesObsolescence here is relative to the opponent and mission. The Rivadavia- and Minas Geraes-class ships were outclassed for a contest with the Royal Navy or United States Navy, but neither fleet acquired them for that purpose. They remained adequate counters to the neighbouring South American navy each state actually planned against. The exchange is a compact lesson in evaluating warships within their regional balance of power rather than against an abstract global standard.