I think part of the problem is that people are assuming that the technology needed to destroy us is much more advanced than is the actual case. In reality all they would need to do is drop rocks on us from orbit.
Look up the kinetic bombardment AKA "rods from god" weapon theory. The original idea, if I recall, was simply to get some telephone pole sized tungsten rods into high orbit, and then just drop them on targets. They calculated the force from kinetic impact would equal about 11 tonnes of TNT, just short of Little Boy.
So, realistically, all they would need to do is show up, grab whatever dense elements they could mine from the asteroid field, move into orbit and then just drop it on us.
Alternatively they could just "push" asteroids into us from the belt without ever actually revealing themselves.
And neither of those options requires technology more advanced than what would be required to travel between solar systems.
Look up the kinetic bombardment AKA "rods from god" weapon theory. The original idea, if I recall, was simply to get some telephone pole sized tungsten rods into high orbit, and then just drop them on targets. They calculated the force from kinetic impact would equal about 11 tonnes of TNT, just short of Little Boy.
So, realistically, all they would need to do is show up, grab whatever dense elements they could mine from the asteroid field, move into orbit and then just drop it on us.
Alternatively they could just "push" asteroids into us from the belt without ever actually revealing themselves.
And neither of those options requires technology more advanced than what would be required to travel between solar systems.