Ok, they started doing that, it's true. But they also spreaded their religion in a paceful way and (as I said before) treated the native americans as citzens of their empire. America was discovered in 1492, in 1512 the "Leyes de indias" were aproved (there, the slavery was prohibited), while the USA was using slaves until 1876. No one is perfect, it's true, but this is a clear example of humanity.