Argentina is the second largest country in South America and features a little bit of everything, from mountains to coastline. Its national team reached the Quidditch World Cup quarter-finals within the last century (QA8). The Patagonian desert region of Argentina was also host to the 2014 Quidditch World Cup (QWC).
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The official name of the country is the Argentine Republic (Spanish: República Argentina) and it is located in the southern half of the South American continent (Wikipedia).
Writing by J K Rowling on Imgur (Daily Prophet coverage of the 2014 Quidditch World Cup, originally from Pottermore):