I've decided to put this thread here in the "SciFi" category, since it involves serious speculation. There literally has been a ton of alien-invasion stories over the years, whether in print or on film. However, relatively few of them seem to have been serious efforts involving logical extrapolation. What I'm wondering is, could there be a plausible alien invasion? Some more specific questions include: What reason(s) or motivation(s) would the aliens have for coming here in the first place? What assumptions are necessary for them and/or their technology? What type(s) of tactics would the aliens use in their invasion? Could there be any real way to repel the aliens? I have plenty of my own thoughts here, but I would like to see some others post theirs first before joining with my own. Serious replies only, please.