How does the land to the east of the Andes differ from the land of the west?
Andes is longest and one of the highest ranges in the world and mind that it matters a lot.
when moisture laden clouds from Pacific enter South America they are no sooner stopped by these mountains . thus all the rains fall on the East side .furthemore, the rich volcanic soil provides area for vegetation and healthy population.
almost nil amount of those clouds are able to cross those mountains and so the area becomes very dry and waterless. it has already given rise to Atacama desert and severe water shortages in countries lying there.
however the land is blessed with the Amazon making survival possible