A class conflict between the Mulatto and the rest of the Haitian people. There was a two class caste system that allowed no upward mobility. Haiti was also massively in debt after declaring their independence and they did not pay off their debt until 1947. This caused major underlying unrest and instability.
What was a factor keeping Europeans out of interior Africa until the late 1800s?
Disease
Rough ground
Dangerous animals
There are three supreme gods in the Hindu triumvirate. First, Lord Brahma is responsible for the creation
of the universe. Second, Lord Vishnu has the duty of protecting and maintaining
the universe. And lastly, Lord Shiva, who is the god of destruction.
The answer to this really depends on what prism you are viewing it from?
As a globe, we are pretty opposed to imperialism these days. China has started to dabble a little more in the South China Sea but we mostly have our nation states and there isn't really a lot of movement.
That was not the case at the time of annexation.
So, is it ethical to subsume a sovereign nation? No
Was it strategically justifiable at the time? Yes. If the United States had not annexed Hawaii, the Empire of Japan likely would have stepped in.
Hawaii has enormous strategic value and was then justifiable at the time of annexation.
That being said, and I hope this is an obvious statement, imperialism is not a good thing and is ethically problematic.