First of all, Peru and Bolivia had vivid memories of the War of the Pacific and how they lost to the superior Chilean navy. Bolivia lost its entire coastline and hasn't really recovered ever since. Argentina and Chile had a bone to pick for centuries, even before they were independent, when they were still under Spanish rule (Chile was part of the Viceroyalty of Peru, Argentina was part of the Viceroyalty of Rio de la Plata, both were separate political entities), and both wanted control over Patagonia (in the end, Argentina got the better share, although the southernmost tip of South America, Cape Horn, still went to Chile). Bolivia had lost the Chaco region to Paraguay during the 1930s (even though their military was larger and better-equipped, they knew nothing about the region's geography, and the Paraguayans were more motivated), and that also dealt a great blow to Bolivian national pride (no coastline, no Chaco region, no Acre, they had lost almost half their territory from independence until WWII). Brazil and Argentina, natural enemies from the start, obviously competed for dominance over the continent, and influence over disputed Uruguay and vulnerable Paraguay. With Colombia and Venezuela, you have two countries with pretty much equal proportions of European, African, and Amerindian influence, you have two countries that didn't want to get involved in the affairs of other nations in South America, yet you have two countries who not only get in trouble with the United States quite often but you also have two countries with constant population exchange. I'd put it this way: It would most likely be Brazilian-led bloc with Ecuador, Chile and Paraguay against an Argentine-led bloc with Peru, Bolivia, and Uruguay. Colombia and Venezuela would be neutral outsiders. How the United States, Europe, Cuba, the Soviet Union, and China would view this situation I don't know, but this is my best idea of an "alliance system."