I can say this much about an invasion from space
It won't happen like Hollywood tends to portray it.
All an ETI needs to do is fling a starship at Earth (or maybe just a big hunk
of metal/rock) at relativistic speeds. The impact will sterilize everything on
our planet.
No need for fleets of invading warships filled with aliens toting laser rifles.
I am sure if we've thought of this, someone out there has as well.
This assumes they consider us some kind of threat to begin with.
BTW, the above scenario is not necessarily going to happen, but it is one
easy, quick way to clean off a planet. Maybe we will end up doing this to
some poor civilization that has some shiny rocks we want.