I am not defining it society is. Cannibals are fairly easily overtaken by non-cannibals so cannibalism is a problem.
Yeah, but they're not overtaken
because they're cannibals. They're overtaken due to a large technological gap.
I am saying monotheism is more complex because it has saturated every wildly successful culture of the modern age, and cannibalism seems to have had a much less successful track record.
Japanese culture is not at all saturated with monotheism, but I'd say they've been fairly successful. Shinto (and all its mixtures with Buddhism by now) is not exactly simple, either. I guess it depends on where you set the bar.
As for the cannibalism, well, the Aztecs practiced some ritual cannibalism during human sacrifice. It wasn't a huge part of anyone's diet, but it was there. As for how good its track record would have been as the centuries wore on, we we'll never know. It wasn't exactly detrimental up till that point, though.
Sure it did, and did so for centuries as their superior organization allowed their empire to expand past their ability to sustain it.
Eventually their society lost the spark that made it so good and they fell apart.
Corruption and the inability to sustain an empire built on conquest and expansion is a problem.
Right around the rise of Christianity, interestingly enough. Though the Eastern Empire managed to make it a lot further, the Western Empire spend a little less than 200 years Christian before collapse.
No, they didn't have time for that, it had to do with some monotheists who had invented guns and and intercontinental travel.
With technology taken from a bunch of Chinese pagans.
They were crushed by a handful of soldiers.
Not quite. The Spaniards had a few things going for them, and certainly did NOT conquer the Aztecs on their own.
First, they didn't do it on their own. They went around and stirred up anger amongst other tribes and cities in the region. They went about manipulating the Aztec's enemies into various alliances and used all those different alliances to their advantage. Just from memory, I want to say the biggest contributor here was Tlaxcala. There would have been massive armies of natives marching with the Spanish.
Second, disease. Cortes arrived in Mexico in 1519, but didn't actually lay siege to the capital until 1521. By the time Cortes waltzed on into Tenochtitlan, most of the city, and indeed much of the countryside, had been ravaged by smallpox and the starvation that followed.
Then of course there was the almost perfect timing of the landing, which coincided with when they were expecting the return of a Quetzalcoatl from the east. That threw them off for a little while before they figured out that these were just more men.
Finally, the hierarchy of the empire itself lent to the Spanish stepping in and replacing the guys at the top and largely letting business continue as usual.
Had the Spanish not walked into a sort of perfect storm of circumstances, the Aztecs would have thrown them back into the sea.
Isolation and ignorance are problems.
Only when some outside group takes it upon themselves to come along and "liberate" you.
Then explain why societies develop more stringent morality as the society becomes more complex.
What do YOU think is the driving force here?
A more complex society requires a more complex set of ethics to operate effectively. The Aztec Empire was fairly large and complex; the capital city of Tenochtitlan was easily larger than just about every city in Europe. Their morality did not stop them from becoming complex, and their morality was not the cause of their downfall.