According to the Drake equation there may be millions of planets within our galaxy (the Milky Way) capable of supporting life with a fraction of those supporting intelligent life and a smaller fraction supporting advanced civilizations that may have the capability to cross interstellar space and reach Earth or may be close enough that a multi year journey to get here at sub-light speed is either desirable or achievable bearing in mind that we have been openly broadcasting to all and sundry for a quite some time and there may well be aliens that can listen in and are within the sphere of the signals we are sending out (about 75 or so years worth).
So, the question is, if there is an advanced civilization out there, would it or could it invade and destroy us?
If that civilization already exists and is able to reach Earth (which many believe has already happened) then we are probably safe.
Why? Because if they could get here and were belligerent or wanted to invade, they would have already done so since we would not be able to stop them.
If they haven't already visited and do exist and could visit then we better hope they are peaceful since they won't want to wait for us to catch up with them to make it a fair fight!
This is a scenario that could, maybe, happen but, for right now, appears to be more fiction than reality.