The term 'gringo' or 'el gringo' actually dates back to the 1806/1807 British invasion of Argentina. Spain, then a French ally (remember that it was a combined Spanish-French fleet that Nelson attacked off Cape Trafalgar in 1805) was at war with Great Britain and one way of hitting back was for the Brits to attack the Spanish colonies in South America.
The British armed forces at that time had a marching song "Green grow the rushes, OH", and this led the locals to call the Britons "Los Gringos". Nowadays, the term is more often applied to US and Canadian citizens.
Hey el gringo, say hello to my little friend!
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