first off...great movie, but thats off topic. Why would they war with this. Surely they understand that they could use other resources from other planets in our galaxy other than our planet.

i dont think its necessarily off topic when discussing the reasons for aliens to invade a planet, wasnt it the first movie to suggest that the need for resources was the reason?

anyway, there would be a number of reasons. slave labor, a planet that is easy to live on, a need for water or other raw materials that aren't easily accessible on most planets. or even a religious reason like "we are the only creatures that are supposed to be alive in the universe because our god says so" type deal.

lets just say its more likely than most think

no, im not saying that the movie is off topic, im saying that the statement "Great movie" isnt about the topic, and any race that gets to our front step has probably far surpassed the social , science, and political setbacks caused by religion. They also will have had many other planets just like earth tho ( I think...dont quote me on it if they attack us lol)