 When Chileans and Argentines of European descent studied, invaded and settled on the islands in the mid-19th century, they brought with them diseases such as measles and smallpox for which the Fuegians had no immunity.The Fuegian population was devastated by the diseases, and their numbers were reduced from several thousand in the 19th century to hundreds in the 20th century.As early as 1878 Europeans in Punta Arenas seeking additional sheep pastures negotiated to acquire large tracts of land on Isla Grande de Tierra del Fuego from the Chilean government just prior to Argentina and Chile's sovereignty here.