The mighty Incan Empire of South America flourished between 1200 and 1535 AD. They developed drainage systems and canals to expand their crops, and built stone cities atop steep mountains such as Machu Picchu (above) without ever inventing the wheel. Despite their vast achievements, the Incan Empire with its 40,000 manned army was no match for 180 Spanish conquistadors armed with advanced weapons and smallpox.
