Movies such as Independance Day, Transformers, War of the Worlds, and the recent Oblivion have aliens coming somewhere else in the universe to conquer Earth. Most of the time its to gain natural resources or because Earth is located in the Goldilock zone around sun had as liquid water on its surface. Still, Why do aliens always seem to be targetting Earth?
Why dont any of them settle on Mars or harvest natural resources from asteroids in the asteroid belt? If these aliens need oxygen and fresh supply of water, they could get it from comets or from one of the gas giants moons. Maybe they need Iron, Carbon and other elements to make alloy metals, Mars, Ceres or 4 Vesta would be a good place to look, with them having much lower gravitational field it would be easier to get it off. If aliens were seen settling down on Ceres or gathering natural resources, any kind of resistance would be nil.