Take some money-grabbing Spaniard empire builders - mostly the unskilled, uneducated and unwashed merely chancing their arm for the odd fortune or two - and plant them, and their smallpox, in one of the brightest, gold-enhanced civilisations the world had ever seen. Give them all egos, flaws, ignorance of how best to go about things, but some outstanding fortune against huge odds when it came to battle, and stir. Thus you get the Conquistadors - never more than two hundred of them for their first few years - against the might of the fresh, powerful, rich and exceedingly well organised Inca empire.