 For nearly 300 years, differing interpretations of the Treaty of Tordesillas led to border disputes between Spain and Portugal over the Río de la Plata region.Portuguese encroachments in the Río de la Plata allowed their merchants to evade commercial restrictions imposed by Spain on the importation of goods into Spanish South America, with Buenos Aires becoming a major centre for smuggled goods.The two countries attempted to finalise their borders by the 1750 Treaty of Madrid but in 1761, it was annulled by the new Spanish monarch Charles III.