Question

Look at the following short outline for an explanatory essay. What is wrong with it? Claim: The Aztec Empire achieved greater developments in government, society, and culture than the Inca Empire.

Answer 1

The problem with the presented outline of the "explanatory essay" is that it creates a comparison between two Empires - the Aztec Empire together with the Inca Empire. The short outline doesn't provide an explanation of any kind, just a comparison. This is the main problem with it. 

Answer 2

An explanatory essay is an essay that presents a view ("explains") or a situation, but which does not analyze it and which also does not make any claims about it.
In the present outline we see an argument, or a comparison: one thing is claimed to have been greater than another.
This would rather be a Comparison and contrast essay.