I always figured the arrival will take shape along the lines of the Europeans’ showing up on the shores of the new world.
Great puzzlement, caution and observation, hiding behind rocks and trees, then outreach and a couple nice dinners.
But somebody will steal something or shoot somebody...and the slaughter will begin.
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Maybe they operate under a sort of Star Trek like non-interference directive. Observe, but don’t interact. Or perhaps the UFOs that have been buzzing US warships are their equivalent of some crazy teens out joyriding in dad’s car in the middle of the night.