You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
(Because there are far too many threads about who won the war of 1812)
So, Spanich and Portugal had been fighting for what's no Uruguay since the begining of the colonial days, a dispute that was ingerited by Brazil and Argentina. The place was under Spanish/*Argentinean control most of the time, but changed hands often.
By 1825, it was under Brazilian control. In 1825, uruguayan rebels crossed to Uruguay from Argentina and called a Congress of delegates from all over the Eastern Bank (that-s how Uruguay was called in Argentina) which declared independence from Brazil, while reaffirming its allegiance to the United Provinces of River Plate. Argentina accepted to incorporate the province to the country. In response, Brazil declared war on the United Provinces.
After the war it became and independent country, belonging to neither Argentina nor Brazil.