4 ideas
A German balloon expedition seeking the North Pole finds a Martian base on an island there. The Martians, who call themselves Nume, hover a ring-shaped station above the Pole using gravity-cancelling technology, and they rescue the explorers. After a British warship fires on Martian airships, the Martians crush British naval power and extend a 'protectorate' over the Earth, and the first contact turns into occupation.
The Martians try to educate humanity into rational morality by protectorate and compulsion, and the project fails. On the Kantian view the novel dramatises, a moral act counts only if it comes from the agent's own self-legislation. A people coerced into virtue gains obedience, not morality, so benevolent tutelage defeats its own stated goal.
The Martians arrive more rational and ethical than humans. Once they rule, their officials start treating the 'Bate' (Earth people) as lesser beings and put control ahead of their own principles. The mechanism is structural: unchecked dominance changes the ruler's character, so claims of superiority cannot justify ruling others.
Put a technologically superior outsider in the coloniser's role, and the reader's own nation sits on the receiving end of the 'civilising mission' it applies to others. Reversing the positions exposes the self-serving logic of imperial benevolence that stays invisible from the ruling side.