> They wouldn't need generation ships. You "just" need sufficient tech to put engines on a suitable astroid and accelerate it to a decent fraction of c; it only needs enough logic to fine tune the path. An invasion force is horribly inefficient vs. just slamming a lot of mass at someone at high enough speed.

I misplaced a link and the name of an author of a sci-fi novel in which space battles are much more science based than the usual laser-tag shoot off. I'll dig through my bookmarks and hopefully post the name in the reply when I get to my pc..

I think there was also a reddit thread about it sometimes in the past.