This article tells the similarities of Imperialism as well. One being that the Na'vi people are much like the Native Americans, who survive using the environment around them and their hunting abilities. Another being that they were being invaded by the Americans, similar to how Africa was being invaded by Great Britain.
A 4 star rating is not that bad for a movie that has to do with imperialism and the environment. This movie pretty much ties into what Imperialism looks back then and to this day. The film summary almost sounds like a war going on between these two sides.
The Sepoy Mutiny is one way of comparing it to Avatar. Just like how they rebelled because of the violation of their traditional beliefs, the Na'vi people raged against the military force because they destroyed the one thing that is so valuable to them and sacred.
The Belgian King Leopold sent his troops to fight to take over Africa. But it got ugly very quickly. Sooner or later, Europe started to join in as well as France, Germany, Italy, Spain, etc. This was known as The Scramble for Africa.