[estimator7292]

I don't think you have any concept of the technologies involved here.

This isn't a case of who has the biggest gun. This is a case of someone has a gun that can wipe out your entire planet and you have a rock.

No, a planetary society cannot stop an invasion once they're in orbit. It simply is not possible, not with any technology we can even imagine.

You very much do not at all understand the argument you're making.