When the alien ship screamed through the solar system, it disrupted communications between the far-flung human mining ships and supply stations and between them and Earth. So Earth and Luna were unaware that they had been invaded until the ship pulled into Earth orbit, and began landing terra-forming crews in China.
The mining ship El Cavador is far out from Earth, in the deeps of the Kuiper Belt, beyond Pluto, when its telescopes pick up a fast-moving object coming in-system. El Cadaver has a variety of other problems that worrying about an alien ship doesn’t seem important, but in fact, it’s the most important thing that has happened to the human race in a million years. The first Formic War is about to begin.