Me and my roommate were wondering why Brazil is the only Portuguese speaking country amid a mob of Spanish speaking ones.
Since most of the answers seem to only cover the land part of the question, why did the Spanish colonies split into 10 + countries while the Portuguese colonies remained united? Similarly where there ever any movements for a larger united Spanish American nation?
Treaty of Tordesillas in 1494.
After Columbus had returned to Europe and revealed there was in fact a bunch of islands in the way of a direct west route to India (no one knew quite how extensive the islands/land mass was), Spain and Portugal began jockeying for the right to claim the new territories.
By this time Portugal already controlled many of the Atlantic Islands between Europe and the Americas, they were very interested in pressing their claim to all of the land out beyond the western horizon. Spain was of course interested in pressing its claim to the islands Columbus had discovered off the shore of what they believed must be India. Because Portugal was really more interested in India, and Spain was a growing military power, they settled for a diplomatic solution negotiated with the help of Pope Alexander IV which essentially draw a line down the Atlantic and divided the territory between Spain and Portugal.
Really no one had an idea what they were dividing up; which does some way to explain why Brazil- which sticks out from South America and crosses the line of the Treaty of Tordesillas predominantly speaks Portuguese and the rest of South America predominantly speaks Spanish.
The historical sequel to the Treaty of Tordesillas would be the Treaty of Zaragoza wherein the same actors would divide up the Pacific and South East Asia thirty years later.
hi! check out these earlier posts (TL;DR: most significantly, the Treaty of Tordesillas)