I am reading Conquest by Hugh Thomas right now, which is about the conquest of Mexico by the Spanish in 1519.
Cortes has just sailed from Cuba, bound for the unknown regions of central America and Mexico. Officially he is supposed to be establishing trade routes and exploring the region; unofficially he is bound on getting as much booty as possible, as are all his troops (who aren't even paid; their remuneration is basically from looting: the Spanish have a lot in common with pirates at this point in time). He had to leave Cuba in a hurry, to avoid being removed from command after the governor became suspicious he planned to exceed his instructions.
For his trade/conquering/looting mission, these are Cortes' resources:
--10 small ships (actually 11 but one got lost on the way; sailing is not a strong point during this period)
--530 European soldiers, 50 sailors, 4 pilots, 5-10 women, a few hundred Cuban Indians, African freedmen and slaves, 2 priests and a couple of kidnapped Mayan fisherman (Cortes hoped they could serve as interpreters)
--16 horses and a bunch of dogs
--and for weapons (besides swords): 30 crossbows, 12 arquebuses (a very primitive gun), 14 pieces of artillery and a few cannon.
Cortes himself is a short (5'4"), clever man in his early thirties, whose main qualification seems to be his friendship with the governor and his ability to understand Latin. He has never led men in battle and never fought in anything beyond minor skirmishes (and some bar fights, during one of which he received a facial scar).
The idea of conquering an entire empire comprising most of central America and Mexico with this puny force is ridiculous. Yet that is exactly what happened. This is why I find history fascinating; you just couldn't make this stuff up.