It has been discussed several times in the forum, and the general consensus is that Cabral would discover Brazil in 1500 anyway, because his expedition (unlike Cabot's one) wasn't related in any way to Columbus'. Cabral was trying to round Africa and 'hit' America by accident, claiming that "new island" for his king.
Admiral Brown said:
So, the Incas and Mesoamericas might have their numbers reduced through smallpox and other disseases, as these illness spread westwards. But this will be better for them, cause they'll be better prepared when other European arrive (Portugal? Spain? Holand? France? England?).
They might also recieve some European tecnologies from Tupi Indiands in Brazil (who would get them from the Portuguese). May be also some domesticated animals, though that will be harder. (May be the Portuguese bring cattle or horses to Uruguay, it reproduces, and, by the end of the century, these animals reach the Tawantisuyo).
I don't think that there were commercial relations at all between the Brazilian coast and the Inca Empire, so Peru would still be untouched by European knowledge and diseases well after European settlements were growing there. That could change if, at least, the Portuguese or somebody else discovers the Plata River and sails it upwards till meeting some Guarani tribes carrying gold jewels and ask them from where that gold came.
Admiral Brown said:
If Columbus expedition fails, Spain might have focused on Muslim Northern Africa, and left America aside. America may be left for the Portuguese for a while. They'd probably have stayed in Brazil, and left the rest pretty untouched, because they were more interested in their empire in the Indian Ocean.
But not being interested in colonization doesn't left the Portuguese uninterested in seeing what the hell was there. In OTL they sent expeditions to Terranova well after signing the Treaty of Tordesillas, for example.
Philip said:
True, but I could see it going another way. Spain was broke when Columbus set sail. Without the influx of wealth from the Americas, this isn't going to change. Portugal was already rich from its African adventures. More money from the Indian Ocean routes was just around the corner. Add to this American wealth, and Portugal can afford a very nice army.
If for "broke" you mean political divided, yes, by 1492 Castile and Aragon are still different countries, but the dynastical union is closed, and Navarre is doomed because of this.
If for "broke" you mean "bankrupt", that is false. True that American gold and silver were what made Spain
the superpower in the second half of the 16th century, but before the Americas the country was rich compared to other western European nations. Aragon had a Mediterranean trading empire, and Castile could grow vast ammounts of crops and sheeps for exportations (specially wool from the later to England and the Low Countries); Add to them African gold flooding through the Sahara towards Melilla and Granada, as well. Combined, Aragon and Castile were a monster comparable to what had been the big guy through the entire Medieval ages, France. Charles of Gaunt didn't need any American money to bribe the elector princes and take the Imperial Crown, he just raised the taxes in Castile.