> Exaggerating a bit, but I'm fairly sure the Spanish speech was: "if you kill the other guys with your much better weapons, you will reach El Dorado"

And they basically did. Not a singular city of gold, perhaps, but the Spanish looted tens of billions of $$ worth silver and gold from Central/South America between 1492 and 1550. Which is all the more impressive given how little European manpower it took and how low their relative incomes would've been at the time.